The law of conservation of momentum basically means that energy is always conserved and never lost when a collision happens.
Using the formula p=mv ...
Player A would have a momentum of 220 N•S
Player B would have a momentum of 0 because he is not moving
After the collision, the total momentum is still 220 N•S because energy is never lost, but now player A is at 0 and player B took his momentum. Think about it this way, if you bumped into something that wasn’t moving, it would fall and you most likely wouldn’t keep moving.
Elastic collisions are where the objects bounce each other and in inelastic collisions they stick together. I don’t watch much football but if you do this should make sense.
If the players fall down together (they tackle each other and fall? I think) it should be inelastic.
Sorry if this was long and confusing but I really hope this helps! ☺️