Collisioning the crossing routes

Coach,
There are a few things I would try. The first is to stress to them the fun of getting free shots in on receivers. Defensive players as a whole love to get free open hits, at least I know I did. Really stress to them the idea of getting free, legal shots on receivers not really expecting hits. It should be a goal. The second would be to keep track of hits over the middle and good bumps that happen in the game. Then give an award, make something up, something fun like a black jersey to wear during the week for the person who gets the most bumps and hits on recievers on crossing routes. The last one would be to run 7 on 7 drills over and over again. Stop plays in the middle if a receiver crosses without being harrassed to point it out. They may also be not bumping crossing receivers because they don't see them until too late. If that's the case, stress the communication that is needed for zone coverage to be efffective. Make sure the Cover 2 corners are letting the LBs know crossing routes are coming and the LBs to let each other know crossing routes are coming. Communication is very important. I hope maybe one or two of these ideas are helpful. Good luck.