Today while testing our 2017 robot with competition spec bumpers around our wooden practice field we had a failure of a few balls.
This occurred when the balls were squashed between the fabric covered noodle of the bumper and a wooden field perimeter while driving at a low speed.
The balls are broken, with cracks occurring between many holes. The failures are not along the welded seam but spread from the edge of the holes, or crack the bridge between holes. That occurred after a limited impact with the balls. A similar occurrence to the same ball a second time would most likely cause the ball to be in several separate pieces.
It seems like the cracks would be quite difficult to notice when field reset is dealing with 600 balls at the end of the match unless they are physically picking up each ball, and squeezing it to check.
Is this an issue others teams have had occur in testing?
Instead of giving us some wood and nails and saying "build us a box", they're handing us power tools and saying "now make us something cool" - galewind [more] 
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