Noble claims that Piazza had a hairy back when he played for the Dodgers; Noble knows this because he saw Piazza shirtless on various occasions in the clubhouse (not sure if there are photos). Noble went on to explain that when Piazza was with the Mets, Piazza’s back was completely bare — not a hair on it — and loss of hair is a side effect of steroid use.
via Why Marty Noble Didn’t Have Mike Piazza On His Hall of Fame Ballot.