In a perfect world
This kid's going to be a Red Sox fan before he can hold a baseball bat!
Much of your decision will be based on the specifics of the sport, such as where the stadium is and what the fans are like. "Ask yourself some questions," says Devra Renner, one of the authors of Mommy Guilt. "Will people be smoking around us? Will my baby end up with beer spilled on him? What are the seats like -- will I be comfortable with him on my lap for several hours? How hot is it going to be?" Obviously, avoid extreme situations: A three-hour baseball game in the midsummer sun puts your baby at risk for sunburn and heatstroke, and those rowdy fans will keep you on your toes. Your biggest challenge on a nice day will be navigating the crowds weighed down with a wriggling bundle and all of his requisite gear. Go with friends to help with logistics, and you might try arriving and leaving slightly earlier or later than everyone else to miss the throng at its worst.
Cheer for the home team. As long as you can keep your infant comfortable (and out of the range of fly balls or stray pucks), you don't have to toss your season tickets.