sex wrestling
Playful wrestling that turns horribly wrong that through squirming and moving happens to put one in a known sexual position.
Jane begins to tickle Jim, Jim goes to grab Jane's arms but misses and inadvertantly grabs a breast in the process after a moment he recoveres and grabs her arms at that point she squirms and flips her body around in his arms and then we have "from behind" and in an effort to fix this they both struggle and fall to the floor inadvertantly ending up in "missionary" and this is how sex wrestling can occur, and to those not involved become a problem.