Shattering bats are dangerous for both the players and the fans. Why do bats shatter? Why did the incidence jump? 
Source: The Reason Baseball Bats Break Is More Complicated Than You Think Gizmodo, which pulled the story from YouTube’s Practical Engineer.
Comment: In terms of technological knowledge, the shift from ash to maple wood for bats made some of the manufacturing and hitting knowledge obsolete. It took an MLB study to identify the problem. The solution was to adjust a seemingly minor design decision — the direction they place their logo. The intermediate causal variables were the different grain structures of the two woods.
Recently, bat-makers have started rotating their logos by 90 degrees on maple bats, as well as marking the grain on the handles. Bat breaks have gone down about 50 percent as a result
Art and Science in Technology - Roger Bohn's Blog 
From the author of Practical Engineering, where the original information came from. He (apologies, I can’t figure out his name) writes: “Hey Roger, from what I remember from my research, they phased in the recommendations, so I think it was a gradual process. MLB doesn’t keep statistics for bat breaks, so it’s kind of tough to get a good handle on how things changed after the new rules in 2009.”
Chronology is therefore approximately like this:
2001 Barry Bonds uses maple bats to set new record
2002-? 2005? Increasing use of maple bats.
? Problem of shattering recognized, committee to research it formed.
2007 Committee reports
2008 Rules change promulgated.
2009-? New rules phased in, incidence decreases.
My point is that it was almost 10 years from start of the problem, to full implementation of the solution. In many industries, that is typical. And this was dangerous, but afaik it did not cause a single fatality.