What would cause my barely used green bearing to do this?

AUSA66 said
Check the inner race they may have been too tight on the axle & cracked when bearing was installed causing particles to get caught up between the bearing & outer race done thousands of bearings over the years never seen that happen normally the bearing would melt in extreme loading

I would think if the inner race was cracked the bearing should be really lose on the axle ! That’s a good thought tho ! Something to definitely look into tho !