I know it isn't supposed to happen because you normalize for the visiting team, and I admit I haven't run the numbers, but it has always seemed to me that when you look at park factors, teams that can't score end up dragging down the park factors for their park. I've wondered if there is a second level correlation - when teams have inept offences, if the teams playing against them also score fewer runs on average than they might and I wouldn't even be surprised if any such effect could be greater for the winning team on the road. It might be also be weather but otherwise it does seem odd Copa's park factor drops when the Tigers offense is horrible.