baseball rat
n.— «As he became more sure with the bat, as he became the player who hit .300 at every stop, as he settled down on the field and in the clubhouse, his personality came out. Not just the one whose competitiveness can overwhelm veteran teammates, but the serious one, the one Alex Cora refers to as a “baseball rat.”» —“Regained edge, sharper play” by Amalie Benjamin Boston Globe Oct. 2, 2007. (source: Double-Tongued Dictionary)