Former MLB star J.J. Hardy is clearly not going to win any Neighbor of the Year awards anytime soon ... he's decided to build a mini-baseball field in his backyard -- and it's seriously pissed off those who live next door.
Hardy began construction on his own personal field of dreams at his Chandler, Ariz. mansion a few months ago ... and at least one neighbor is so furious over the ruckus it's caused, she went to a local news station to go public with her gripe.