Should the Boston Celtics use their last roster spot to give Simmons a shot? Here's the case for and against the Celtics signing Simmons. Simmons has been a point guard for most of his career, but he could play some small-ball center for the Celtics. Defensively, lineups featuring Simmons, Tatum, Paul George and Derrick White would be very switchable. The Celtics might be better off leaving the roster spot open for someone who is a better fit in Mazzulla's system.