With the money I'm making, I should be playing two positions.

Rose’s quip plays on baseball’s everyday reality—players are paid to perform a single, specialized job—by exaggerating the bargain he thinks his club is getting (or the burden he feels he’s carrying). The humor depends on the idea that salary should scale with workload: if he’s earning “so much,” he jokes, he ought to be covering two defensive roles at once. It also reflects Rose’s public persona as a relentlessly driven, blue-collar competitor who framed his value in terms of effort and availability. The line can be read as both self-deprecating (mocking the logic of pay-for-output) and self-promotional (implying he’s worth even more).