At the 1999 All-Star Game at Fenway Park, I stood on a packed Lansdowne Street behind the Green Monster during the Home Run Derby and watched ball after ball fly not just over the wall, but over the street and onto the roof of the parking garage. Mark McGwire may have blasted one or two that bounced off the garage and onto the Massachusetts Turnpike.
Luckily, no 50-car pileups ensued.
It was great theater. The sluggers were hitting balls in places never before seen at Fenway Park. It was assumed something was up with the balls -- they simply weren't supposed to travel that far -- but it wasn't a big deal.