The miner was using a 4-1/2"" grinder. The grinder bound in a crack and kicked back toward miner's face. When it came in contact with the faceshield miner was wearing, the grinder ""walked"" its way down the front of the shield and then up and under to contact the miner's chin. This caused a cut that required stitches at a local clinic. The miner returned to work for next shift.