Basically, MLB players shifted to the maple bat, which feels 'harder' and facilitates striking the ball for many players, after Barry Bonds had success with it during the 90's. It's now the bat of choice, but with one obvious side effect: unlike old-school ash bats, which just crack in two when they break, maple bats shatter into various pieces when they break, flying everywhere and flying far. We've seen many a player in the field see close calls with maple bat shards whenever one of them has cracked.
Fans have also had close calls, but as the story notes, 50 year old Susan Rhodes wasn't so lucky. Her broken jaw is out of alignment and the side effects of breaking a jaw have left her exhausted and essentially confined to her home.
In light of this, could the usage of maple bats pose a problem down the line? I'm sure the bats have their advantages, but even players are starting to get concerned about the hazards of shatered maple bats.