Paul Pierce -- Hey Doc Rivers ... I Can Explain My Sucky First Pitch

Brand new Clipper Paul Pierce tells TMZ Sports he has answers ... answers as to why he threw what his own coach Doc Rivers called an "AWFUL" first pitch at a recent Dodgers game.

Pierce was out in Inglewood, CA being worshiped at a party thrown by his hometown folk when we asked him about his new play caller's scathing (yet playful) critique of Pierce's skills on the mound.

Check out the clip -- Truth has a perfectly good reason for why he bombed on the first pitch ... and it's one that Doc Rivers -- and Clipper fans everywhere -- will be thrilled to hear.

We feel you Paul ... it was still pretty bad though.