And not in a good way.
On the day that Greene was placed on the disabled list because of social anxiety disorder, the Cardinals shortstop described a long-running pattern of emotional problems in an interview with FanHouse.
"I don't know what level, as far as how much one internalizes the feelings, how deep they go to the core of a person, but for me it's always been pretty deep," Greene said Friday. "I've always taken the game pretty seriously and wanted to perform well. It's been a love-hate relationship in a lot of ways."
Greene said he felt an extreme version of what you might call "butterflies."
"A lot of that is natural and it's a response to what you consider important," Greene said. "A lot of that is healthy, but for me it wasn't healthy in terms of how deep it goes. I don't know how to describe it, other than the fact it wasn't pleasant."
Greene has been undergoing treatment for anxiety for a few weeks, since his problems with the Cardinals started to reach a boiling point. On Friday, he became the second player this season to go on the DL with anxiety. Dontrelle Willis missed the first month and a half of the season for the same reason.
Cardinals manager Tony La Russa said anxiety is not new to baseball, even though it is rare for it to result in a player being disabled.
"This is not a stress-free business," La Russa said. "This is different from a physical injury, so I don't really want to go into it. How I understand it is he's put a lot of pressure on himself."
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When the Cardinals acquired the 29-year-old shortstop last winter, they should have had a clue that he was intense. His 2008 season was ended when he broke his left hand punching a wall in the dugout.
When Greene got off to a bad start with his new team, there was talk that the Cardinals were concerned about Greene hurting himself again.
Greene said that was not really a risk.
"I'm not looking at it along those lines," he said. "It's a moment-to-moment thing. When I'm faced with it, it's really hard and when it's over, it's over."
Greene said he didn't have physical symptoms of anxiety, such as shortness of breath or a racing heart, but he was mentally drained.
"It was difficult to concentrate, difficult to sustain my energy level," he said. "All my energy was wasted trying to control myself. Just trying to get myself to function, to be able to stay in the game and not be thinking so much what I'm thinking. It's just a battle to be relaxed. I'm trying to battle that and find a way to come to terms with that, trying to find those coping mechanisms."
Greene said he had no qualms with the decision to put him on the disabled list.
Although GM John Mozeliak told the St. Louis Post-Dispatch that Greene's time on the DL was "open-ended," Greene said he hoped he'd be back in 15 days.
"They felt it was in the best interest of the myself and the organization," Greene said. "It can be beneficial, get a chance to reflect and work on some things, and come back and be a productive player, which I feel is a realistic expectation."