No, the air conditioning wasn't turned up too high. Byrnes was honoring the memory of a man that is close to his heart.
The cap read "Tillman Team" and bore the No. 42, a tribute to former NFL player and Arizona State University standout Pat Tillman, who gave up his contract worth millions of dollars to volunteer in the Army after the attacks of Sept. 11.
Tillman was tragically killed in a friendly-fire incident in Eastern Afghanistan on April 22, 2004.
Byrnes, who like Tillman is from Northern California, rounded up teammates Dan Haren, Chris Snyder, Chris Young, Doug Davis, Mark Reynolds, Justin Upton, Chris Burke, Brandon Lyon, Chad Tracy, Augie Ojeda, Brandon Webb and Minor Leaguer Tim Raines Jr. to join Team Tillman.
Professional athletes who join Team Tillman pledge to donate a certain amount for on-field accomplishments such as wins or home runs, or they can make a flat monetary contribution to the Pat Tillman Foundation. Fans can get in on the action either by making a monetary donation or choosing to donate a specific amount for their favorite player's on-field accomplishments.
The foundation's goal and mission is to carry forward Tillman's legacy by inspiring people to make positive changes in themselves and in the world around them.
For Webb, the decision to get involved was an easy one.
"He's a hero to a lot of people, especially here in Arizona, but also across the country," Webb said of Tillman. "I'm glad to be a small part in helping because of who he was and what he stood for and gave to our country. The foundation does some great things, and I just wanted to be a part of it as a way of saying thanks for all that he did."
The foundation is holding its third annual Pat's Run on Saturday, where fans participate in a 4.2-mile run around the Arizona State University campus, with the finish line being the 42-yard line at Sun Devil Stadium.
"We feel it's important to contribute," said Byrnes, who plans to be at the event. "This guy did so much for us. This is our chance to recognize that.
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.