I get so sick of hearing arguments like this. We're talking about professional athletes here, not preschoolers playing soccer. If they're really affected that much by the fans being quiet or booing, then frankly they need to find something else to do or somewhere else to play. +1 Kerry Wood, the quintessential "tough Cub player," has publicly admitted that when the crowd gets down on him when he is pitching poorly, it affects him negatively. Do you want him to play somewhere else?