I found the more you make your [tag]baseball practice[/tag] competitive the more the players like it. Even in the warm up throwing drills we see who can catch the most, who can get the furthest apart, (one step at a time, after every catch), and they love it.
To add to that, another idea is to add a prize. Everyone likes to win stuff, and by the end of practice all the players end up winning something, but it seems to add the extra competitive edge and makes them push that much harder.
I usually do a grab bag of stuff, but this year to encourage more speed training and cardio work out; one of my prizes is going to be jump ropes. Each player will end up winning one but they will work like crazy during [tag]baseball[/tag] practice to do it.