Miner was riding the mantrip when it struck a coal rib causing a piece of coal rib to strike a miner in the lower left side back. This accident was not reported to mine management until 03/22/2018. The miner involved worked this shift and the next shift. Miner went to the Doctor on 03/19/2018 and returned to work on 03/22/2018 when they reported this happened at work.