There is a particular category of football injury that physios find both frustrating and funny, and it's the one that happens after the ball has already gone in. Players have damaged themselves in almost every conceivable way while celebrating, and some of the incidents have had genuine consequences for seasons.
Worth going through the mechanics, partly because it's entertaining and partly because a couple of them are more dangerous than people realise.
The knee slide
The most iconic and probably the most consistently risky. A player at full sprint drops onto both knees and slides.
On a wet surface this is fine — the grass gives, the slide is long and smooth, and the deceleration is gradual. On a dry pitch it's a different proposition. The knees catch, the slide stops abruptly, and all that forward momentum has to go somewhere. Usually it goes into the knee joint as a rotational force, which is exactly the mechanism that damages cruciate ligaments.
There's also a straightforward friction problem. A dry pitch will take the skin off a knee through a pair of shorts, and grazes like that get infected more often than you'd think.
The ones that really go wrong are where a player slides into an advertising board, a camera position, or the base of a corner flag, which has happened more than once.
The fence and the wall
Climbing something is the second big category. Fences, barriers, hoardings, the netting behind a goal.
The risk here isn't the climb, it's the coming down, usually with a crowd of teammates arriving at speed behind you. Ankle injuries from awkward landings are common and there have been a few nastier ones — a player coming off a barrier onto a hard perimeter surface rather than grass.
There's also the crowd-safety dimension, which is why the rules exist. A player at a fence draws hundreds of people towards a barrier, and barriers have failed before.
The pile-on
Genuinely dangerous and completely normalised. A goalscorer goes to ground and eight teammates land on top of him.
The person at the bottom is taking the combined weight of several very large athletes arriving with momentum, often on a joint that's in an awkward position. Ribs, shoulders and ankles are the usual casualties. Occasionally somebody's studs end up somewhere they shouldn't.
What makes it worse is that the goalscorer can't brace, because he doesn't know it's coming or from which direction. It's one of the few situations in football where a player is completely unprepared for significant impact.
The corner flag
A specific and slightly absurd hazard. Players run to the corner flag, and then interact with it — kicking it, swinging round it, in one memorable case attempting a martial arts move on it.
Corner flags are more solid than they look. They're designed to stay upright in wind, which means the base is weighted and the pole doesn't yield much. Kicking one at full force is functionally similar to kicking a fence post, and at least a couple of players have picked up foot injuries doing exactly that.
The acrobatic celebration
Somersaults, backflips, handsprings. Performed by players who mostly trained in gymnastics as children and mostly know what they're doing.
The risk is the surface and the boots. A backflip on grass in studded footwear is a different proposition to one on a mat in bare feet, and the landing is where things go wrong — a stud catching on landing turns a controlled rotation into a twisted knee or ankle.
To their credit, the players who do these are usually genuinely skilled at them and injuries are rarer than you'd expect. It's the ones who attempt it once, spontaneously, having not done it since they were fourteen, who end up in the treatment room.
The shirt
Not usually an injury risk, but worth a mention for a different reason. Taking the shirt off leaves the player in a compromised position — arms tangled, vision obscured — while running at speed, occasionally into a crowd of celebrating teammates.
The real cost of shirt removal is of course the booking, and there have been several cases where a second yellow for celebrating has cost a team a match. Whether that counts as an injury depends on how you feel about the manager's blood pressure.
Does any of this actually matter
The genuine answer is: rarely, but occasionally quite a lot. Most celebration injuries are grazes and embarrassment. A handful each season are significant enough to cost a player weeks. And every few years there's one that costs a season.
Clubs mostly don't intervene, and I think that's correct. Telling professional athletes not to celebrate goals would be both futile and joyless, and the injury rate is very low compared to, say, the injury rate from actually playing football.
The one that medical staff do quietly discourage is the knee slide on dry surfaces, and you can occasionally spot a player checking himself mid-run and deciding against it. The rest is accepted as the cost of doing business.
Which seems about right. A sport where nobody ever hurt themselves being too happy would be a worse sport.