If you have front-row seats behind the dugout on the 3rd base side, do not sit your infant on your lap facing left-handed batters. There was a guy at the Rockies game last night who did this, and it made me so uncomfortable -- it would have been a horrifying "told-you-so" moment.
Even though I am judgmental by nature, I at least try to be pretty live-and-let-live about parenting choices (particularly about sports):
I wouldn't bring my infant (the couple brought their toddler, too, not that she was any less safe in those seats), but I certainly wouldn't sit where they did.
Have you ever brought an infant (under 1 y.o.) to a sporting event? How about a toddler? What age is too young? What age is "old enough?"
(PS: After the game, I was at a bar having dinner and wearily left at 11 p.m. Another couple with a toddler was still going strong at one of the bar's tables. Again: They might have their own sleep schedule for their kid, but I couldn't envision it working for me.)
(PPS: I am absolutely not averse to bringing infants or toddlers to bars. In fact, most of Gabe's first 3 months were spent bar-hopping in the afternoons, sometimes just the three of us and sometimes in these weird gatherings of Brooklyn moms... and me.)