An infielder guards second base.
infielder definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
Baseball a player whose defensive position is in the infield; shortstop, first baseman, second baseman, or third baseman: the pitcher and the catcher are considered infielders when fielding the ball
infielder definition by American Heritage Dictionary
A player assigned to the infield.