Define ballhawk
For him or in general?
For him, he uses his speed and athleticism to pressure the opposing player and try and take them off the ball or rush them into making a decision. While he's very good at "chasing the game" he is mediocre from a positioning standpoint and can sometimes over-extend. This is an issue when you have a poor defensive formation and FBs that push up the field like we do.
In general, a ballhawk should pressure the opposing player and force them into poor decisions. He should use his positional awareness and IQ to force mistakes instead of just his legs or athleticism.
That is something that Lopez lacks, but for $51,500 a year, that first player I described is pretty good to have for 20 minutes a game.