Player two who was signed in on a different controller was completely idle for me.
As the author above suggests you press
to jump. You must do this 500 times, they do not all need to be in the same round. You will likely get this through normal completion of grinding the other achievements so it is advisable not to grind it. This achievement IS Glitchy.
End of jumping for the level on my account, I got the WINNER achievement on player 1 (my login) but did not get the Jumper achievement and for some reason player 2 who was idle the entire time DID get it.
double checked logins, it just did not make sense. O_0 also as reported, the tracker doesn't seem to work for this achievement and they DO pop AFTER the round. not sure if you can quit out, I just played them out.
EDIT 5-18-17 I speculate the reason it was bugged for me is that I tried unlocking it on my girlfriends home console... I am going to try it again by installing the game on my console and will update. I suspect that this will affect very few players but keep it in mind if you're playing on someone else's console for whatever reason