Entity cant ride player

I was working on a mod, and I made a procedure that checks when an entity is hit, and if my entity hits the entity, it will start ridding it.
The problem is that it doesn't work; my entity will just stand still looking down. If I try it the other way around, where the hit entity rides my entity, it works, as does using one of the entity's built-in triggers. I don't understand what is wrong with the code.