Problem with top trums for players is the fact that many of the good things players do can not be quantified.
For example, you can be one of the best back players around and not really shoot too many people, because you are keeping the other team's heads in and protecting your own players.
Problems also come when you look for stats like games alive at end...players eliminated...etc.
It could work but would take a lot of effort!
Some simple ideas however;
Age
Height
Weight
Years playing
Agression level (like the poison level on the snakes etc they have)
Number of events won at pro level