A player below 100 usage cannot be overused but you are probabaly confusing his Stolen Base (SB) overuse. You may want to read the STATUS section in the manual which explains each heading on the status page (a crucial page in your understanding of the game---and excellent reading).
Also: A player can not be rusty if he has recently been used. More on RUSTY status in USAGE/LIMITATIONS section fot he manual.

Mike Bravard (PB)