This season, MLS has become a bloody place. Four of the league's most dynamic attacking players — Seattle's Steve Zakuani, Dallas's David Ferreira, Salt Lake's Javier Morales and DC's Branko Bošković — have suffered horrific injuries, totalling six broken bones, a dislocation and severe ligament damage between them, leading to a torrent of discussion about the physical nature of play in MLS. Detractors insist that the league suffers a plague of thuggery; that skilful players are being fouled out of the game and that offenders should be drawn and quartered. Others take the position that soccer is a "man's game", that accidents can and will happen and chalk it up to bad luck. 

Adrian Hanauer, the general manager of Seattle Sounders, for instance, was outraged by the foul by the Colorado rapids midfielder Brian Mullan that cost Zakuani most of this season. "I think maybe a good answer is Mullan gets to play when Steve is back on the field. He's a hard player, but that was a dirty tackle. He lined him up. There was absolutely no reason to crush him like that. It's my hope that he'll be heavily punished, but obviously it's out of our hands." Goal.com's Jermey Horton waded in, asking "when is the league going to do something about this? MLS is becoming unwatchable - soon only the thugs will be left standing."

Mullan himself, having been given a 10-game suspension, insisted it was just bad luck. "It was never my intention to injure him," he said. "It's a tackle that I've done hundreds of times and would probably do again. I had no intention of hurting him. It's a freak, freak thing, and I apologize and wish Steve a speedy recovery." Teammates, meanwhile, hastened to offer the 'not that kind of player' defence. "I feel bad for Brian," said Jamie Smith. "He has been in this league long enough that everyone knows that's not Brian's character, that's not how he plays."

The stances, of course, are not mutually exclusive. It's accepted that the US college system has a tendency to scout and produce athletes rather than footballers; attributes such as size, speed and endurance tend to outweigh some of the more technical aspects of the sport. Finesse skills, such as control, composure, and game intelligence tend to be marginalised, often leaving a shell of a footballer, physically competent if mentally deficient. While the college system itself is playing less of a role in the distribution of talent to the league than it used to, it still plays its part in the selection and development of a large swathe of potential candidates. Physicality in the negative sense implies a recklessness or violence, but it may be that MLS's physicality lies more in the athletic nature of its players, who at times put themselves in difficult positions and make bad decisions. 

One aspect of MLS alien to European football is the level of inequality that can be found on any one pitch. In Europe all players are funnelled through a complex, successful system that distributes the players based on skill; a player with top-level skill, classed as A, will rise to the top, a player of slightly less skill, a B, will play lower, and so on for those of levels C, D and E. In a pyramid system, a top team will feature A-rated players, sprinkled with some Bs, the tier below will have some B-rated players with some Cs, and so on. In short, every player, over the course of time, will find their level. There will be some migration as experience, age, and injury can affect level, but equilibrium will be struck. In MLS this just doesn't happen as a result of the salary cap. It's not uncommon to have a team consisting of one or two As, a handful of Bs, some workhorse Cs with even a D or E on the field and almost certainly some on the bench. Such a disparity in talent, non-congruent pieces trying to fit together, cannot create a peaceful whole; there will be instances where a clash between the differing natures will cause problems, usually resulting in sloppy play and frustration, but in extreme cases, physical harm. 

Another factor to consider is the 2011 calendar. Due to the increased number of teams, the maintenance of the balanced fixture list which is good and essential) and the Gold Cup in the summer, each team has had to contend with a heavy schedule. Toronto, for instance, played 11 games in 35 days from April 23. MLS Cup finals have been inching deeper into the winter, while First Kick has been pushing forward into the spring, compressing the offseason; meanwhile the additional league matches and expanded competitions, such as the Concacaf Champions League, not to mention the interminable midseason friendlies, have increased the fixture congestion to an impractical extreme. Limited squad sizes, a lack of quality replacements and the subsequent overreliance on certain players, added to the external factors such as travel, climate variation and the relative — to their European counterparts — lack of reassuring compensation, the life of an MLS player has become rather hectic. It's conceivable that these injuries have resulted from physical and mental fatigue. Player fitness functions much like a mathematical wave, a peak in performance will be followed by a trough; the aim is to peak at certain times in the season, but inevitably there will be down periods. That many matches ended in draws — half of the 22 games played between May 4 and May 15, the eighth and ninth weeks of the season — implied that players had hit their first fitness plateau of the season, resulting in a downturn in effectiveness. Inevitably, when a player becomes fatigued, the ability of the body to absorb impact diminishes and tackling becomes less precise, which has the dual effect of making a player more susceptible to injury and more likely to encounter a situation that could cause injury.

The suspicion is that refereeing too has suffered in this expanded season. As Bošković ominously put it in autumn 2010 after five months in the league, "The referees in the USA are different. What they decide is a foul in Europe is not in the USA; they have to hit you hard for it to be a foul." While leniency is difficult to quantify, consistency can be; of the six officials with at least 100-matches completed the discrepancies in number of fouls awarded (25.2 to 29.2) and yellow cards shown (3.2 to 3.8) per match raise few concerns. Those for red cards (0.168 to 0.402) and penalty kicks (0.234 to 0.393) — events that can drastically affect the outcome, style and mood of a match — though, are worrying. That the opposite ends of the spectrum are embodied in two officials, Abby Okalaja (low) and Baldomero Toledo (high) is more troubling still. Okalaja (27.2 fouls per game; 3.3 yellows) appears happy to call fouls but is reluctant to make game-changing decisions, while Toledo (25.2; 3.7) regularly alters the match with expulsions and penalties. Another referee, meanwhile, Jason Anno, showed 16 red cards in his first 24 matches.

The figures may be down to bad luck rather than incompetence, but the suspicion is there is no proper investigation as the pool of referees is controlled not by MLS but by the US Soccer Federation. It issues pre-season guidelines emphasising a particular action it wishes to remove or encourage (contact to the head and attacking impetus, for instance, have been targeted recently) and at the beginning of the season promoted five first-year referees who were inexperienced in high-level matches. There has at times been a sense of general confusion exacerbated by poor match management, which has frustrated players who do not feel confident in the authority of the match official and so have on occasion taken justice into their own hands. 

It should be noted that the most subtle of the four tackles that have provoked the debate, the Ferreira injury, happened on a synthetic pitch. Although technology in surfaces and boots has improved drastically over the past few years, the possibility of a catastrophic failure, a clash of man and surroundings, still exists. Some argue that the severity of this injury was due in large part to the boot catching in the turf, exerting additional force to the stress point that would have otherwise been dissipated by a natural surface, possibly avoiding the fracture. 

MLS's reputation as a physical league is well deserved: players are superb athletes, capable of maintaining a high level of play throughout a long season; they have to put up with countless hours of travel, crisscrossing time zones and enduring the kaleidoscopic climate variability of North America, but the implication of the negative insinuations of the word is to simplify the problem these injuries should be used to highlight. It would be folly to blame random chance for such a catalogue of injuries. Luck has played its part, but there is also an array of background factors, some easily reconcilable and some that require longer-term treatment. Injury is inevitable in all sport, but for its own development, MLS must create an environment in which the best players do not live in fear.