How Do ACL Injuries Happen in MLS? A Breakdown of the Most Common Mechanisms in Men’s Soccer

The anterior cruciate ligament (ACL) is one of the most feared injuries in professional soccer, capable of ending careers or sidelining star players for months. In Major League Soccer (MLS), where physicality and speed collide on every play, ACL tears remain a persistent concern—despite advances in training, equipment, and medical care. A groundbreaking new study, published as part of a systematic video analysis, has now dissected the precise moments when these injuries occur, revealing patterns that could reshape how coaches, players, and medical staff approach prevention.

Unlike past research that relied on player recollections or broad statistical trends, this analysis used frame-by-frame video breakdowns of actual ACL injuries in MLS to identify the exact biomechanical triggers behind the most common mechanisms. The findings challenge some long-held assumptions about how these injuries happen and highlight critical moments where interventions—whether rule changes, training adjustments, or on-field tactics—could make a difference.

For players, coaches, and fans alike, understanding these mechanisms isn’t just academic. It’s about reducing risk, extending careers, and preserving the integrity of the game. Here’s what the data shows—and why it matters for the future of MLS.

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What the Study Found: The Three Most Dangerous Ways ACL Injuries Happen in MLS

The analysis, which examined dozens of ACL injuries across multiple MLS seasons, identified three primary mechanisms responsible for the majority of tears. Each scenario involves a unique combination of player movement, opponent contact, and environmental factors. The key insight? Most injuries don’t occur during high-speed collisions but rather in deceptive, split-second decisions where players misjudge direction, balance, or the position of their limbs.

Here’s how they break down:

1. The Non-Contact Landing Gone Wrong

Contrary to popular belief, only about 30% of ACL injuries in MLS involve direct contact with another player. The rest happen when a player’s knee buckles under their own body weight—a failure of the joint to absorb force properly during landing or cutting.

How it happens:

• A player jumps to head a ball, lands awkwardly, or pivots sharply while their foot is planted.
• The knee collapses inward (a movement called valgus collapse), stretching the ACL beyond its limits.
• Often seen in midfielders and forwards during 50/50 balls or when chasing rebounds.

Real-world example: In 2023, Seattle Sounders midfielder Jordan Morris suffered a season-ending ACL tear after a seemingly routine jump for a header. Video analysis later showed his knee rotated inward as he landed, with his foot planted in a way that created excessive torque on the ligament. There was no contact—just a biomechanical failure.

Key takeaway: Strengthening the quadriceps and hamstrings (to stabilize the knee) and improving landing mechanics (e.g., bending at the hips, not the knees) are critical for prevention.

2. The Side-Step Cut with a Twist

This mechanism accounts for roughly 40% of non-contact ACL injuries in MLS and is particularly common among defenders and wingers who rely on quick directional changes. The danger lies in the combination of lateral movement and rotational force—a move that looks routine until the knee gives out.

How it happens:

• A player is running forward and suddenly cuts sharply to the side (e.g., to shield the ball or change direction).
• The outside foot pivots while the inside knee remains fixed, creating a shear force that stresses the ACL.
• Often occurs when the player is fatigued or has already made multiple cuts in quick succession.

Real-world example: Los Angeles FC defender Yan Couto tore his ACL in 2022 during a 1v1 duel with a forward. The video showed him executing a side-step cut, but his knee rotated beyond its stable range, resulting in a complete rupture. Notably, he had already made three similar cuts in the previous 30 seconds—a pattern that suggests fatigue-related decision-making played a role.

Key takeaway: Coaches now emphasize controlled cutting drills that teach players to decelerate before changing direction, rather than relying on explosive lateral movements.

3. The Collision with a Hidden Opponent

When contact is involved, the most dangerous scenario isn’t a high-speed tackle but rather a misjudged slide tackle or a collision where the player’s knee is bent and vulnerable. These injuries often occur in tight spaces, such as near the penalty box or in congested midfield battles.

How it happens:

• An attacker dribbles past a defender, who reacts by sliding in with their foot extended.
• The attacker’s knee is bent at the moment of contact, and the force of the tackle drives the tibia forward.
• Alternatively, two players collide while both are moving laterally, and one’s knee absorbs the impact.

Real-world example: In 2021, Columbus Crew forward Darwin Cerén suffered an ACL tear after a seemingly routine challenge. The video revealed that the defender’s sliding tackle caught Cerén’s knee at an angle where the ligament was already stretched—an injury mechanism that’s difficult to avoid without better spatial awareness.

Key takeaway: Rule refinements, such as MLS’s “no sliding tackle within 18 yards of goal” policy, have reduced some contact-related injuries, but the study suggests that player education on safe tackling techniques remains essential.

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Why These Mechanisms Matter: The Human and Financial Cost of ACL Tears

ACL injuries aren’t just a medical concern—they’re an economic and strategic nightmare for teams, players, and the league as a whole. Here’s why understanding these mechanisms is more than just academic:

The Career-Altering Impact

An ACL tear typically requires 9–12 months of recovery, including surgery, rehabilitation, and a gradual return to full contact. During that time:

• Players lose 10–15% of their muscle mass in the affected leg, requiring extensive strength training to rebuild.
• Many never return to their pre-injury level of performance, with studies showing 20–30% of professional soccer players don’t play at the same standard after an ACL reconstruction.
• Psychologically, the injury can be devastating—players often fear re-injury, leading to hesitation in decision-making.

Example: Former MLS star Dwayne De Rosario returned from ACL surgery but never regained his explosive pace, ultimately retiring at 33 after a second ACL tear. His story is echoed by countless players who face the reality that career longevity in soccer is often measured in ACLs.

The Financial Strain on Teams

For MLS clubs, an ACL injury isn’t just a loss of a player—it’s a financial hit that can ripple through the entire season:

• Medical costs: Surgery and rehab can exceed $50,000 per player, not including lost wages.
• Transfer market disruption: Teams often accelerate the sale of injured players to recoup costs, disrupting long-term plans.
• Competitive disadvantage: A top player missing six months can mean the difference between playoff contention and a mid-table finish.

Data point: Between 2018 and 2023, MLS teams spent an estimated $20 million annually on ACL-related medical expenses and transfers—money that could have been invested in youth development or player salaries.

The Rule and Culture Shift

The study’s findings have already influenced discussions about how soccer is played at the professional level:

• Tackling regulations: MLS has expanded its “no sliding tackle” zones and increased penalties for dangerous challenges, though enforcement remains inconsistent.
• Training innovations: Clubs are now prioritizing plyometric training (jump training) and balance-board exercises to improve knee stability.
• Player education: Programs like the MLS Player Safety Initiative now include modules on recognizing high-risk movements.

Expert perspective:

“What this study confirms is that ACL injuries in soccer are not random—they’re predictable based on movement patterns,” says Dr. Emily Carter, a sports biomechanist at the American Sports Medicine Institute. “The challenge now is translating that knowledge into real-time coaching cues. For example, if we can teach defenders to slow down before cutting or attackers to land with softer knees, we could see a 20–30% reduction in non-contact injuries.”

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Common Misconceptions About ACL Injuries in Soccer

Despite the volume of research, several myths persist about how ACL tears happen—and how to prevent them. Here’s what the data actually shows:

Myth 1: “ACL injuries only happen in high-speed collisions.”

Reality: Only about 30% of ACL injuries in MLS involve direct contact. The rest are the result of poor landing mechanics, fatigue, or overuse. The study found that players were often injured during low-speed movements, such as a routine turn or a jump for a header.

Myth 2: “Bigger, stronger players are less likely to get ACL tears.”

Reality: While strength helps, poor movement patterns are a bigger risk factor. The analysis showed that even elite athletes with high fitness levels could tear their ACLs if they didn’t control their knee alignment during cuts or landings.

Myth 3: “ACL injuries are just bad luck.”

Reality: The study identified three repeatable mechanisms that account for 80% of injuries. This suggests that with better training and awareness, many tears could be prevented.

Myth 4: “You can’t return to 100% after ACL surgery.”

Reality: While some players experience lingering instability, modern rehabilitation techniques now allow 70–80% of athletes to return to their pre-injury level. The key is structured rehab and gradual return-to-play protocols.

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What’s Next: How MLS and the Sport Are Adapting

The insights from this study are already driving changes in how soccer is coached, played, and regulated. Here’s what to watch for in the coming years:

1. Real-Time Coaching Tools

MLS clubs are experimenting with wearable sensors that track player movement in real time, alerting coaches when an athlete is making high-risk cuts or landings. For example: