For example, WRs have to block for the WR screen to work. As 1980VT points out -- everyone runs this. Why does it work for some teams and not others - watch who blocks and who doesn't.

I was at the PSU/Auburn game earlier this year. PSU had success with their WR screen and Auburn didn't. Auburn's WRs hated to block.

I hate to call out a player from the past, but I remember Marcus Davis not wanting to block on our WR screens. His defender consistently blew that play up because he didn't block his man. Our fans would boo and gripe about the play call. It wasn't the call, it was a player not doing his job. And it was sad, because I thought Davis had the talent -- he just had no desire to block anyone.