When human stampedes occur a person can trip and fall and then another person falls on him and then another person blah bla, or in football when everyone jumps onto each other on the ground to get the ball away from the one on the bottom How would you call that? Human clump
OK, so there are many, many ways to describe human "stampedes", one can say that the players fall down in a heap.
In rugby, this is called a pile. But in regular football (soccer), this doesn't exist. Two or three players may bump into each other but there is no real pile-up. In American football, it's called a pile-up or pile and occurs when players fall over each other in a heap over the player with the ball.
They are squashing each other when on the ground. The rules are different in rugby and American football, but I think pile and pile-up answers your question.
By "football" I assume you mean "American football" since what we Americans call "soccer" doesn't usually involve a lot of clumping (at least, when played by adults)
In addition to the suggestions in Lambie's answer, there are a number of other terms that depend on the context. With football, we call this situation a dogpile, which can be used as a verb to dogpile.
The defense dogpiled the running back to keep him from moving across the goal line.
On a more somber note, when too people people are trying to move in a particular direction, often in a panic, this is called a crush, a human stampede, or a crowd collapse. Unfortunate people can be crushed or trampled by the crowd.
Dr Fruin explained that virtually all crowd deaths are the result of compressive asphyxia and not the "trampling" that is often reported in the media.