I was lead climbing up a corner crack. I got to a certain point and felt uncertain about the moves and couldn't see any obvious places to climb to to place more gear. After much deliberating, I backed off the route. I had what I thought was a good cam placement (I had never been taught that slightly flared cracks horizontal cracks were not suitable for cam placements), I couldn't see anywhere else to place gear and I had more good placements below me. I began to be lowered but the belayer wasn't very experienced and the lowering off was very jerky. At some point my cam popped and I fell around 4-5m before my gear caught me. I stopped just above a ledge but my leg kept moving and whacked the ledge leaving a huge bruise and graze. It was multipitch climb so my partner had to finish the climb. I was stuck on the ledge in a lot of pain from my leg.