If a hernia is the most unpleasant and ligament damage the most painful, then the hamstring injury is easily among the most frustrating for any footballer. Not only can the hamstring emit that infamous 'pop' at any given moment, but it often takes months for a player to fully recover. The injury usually occurs when the muscle in the back of the leg is over-extended, triggering a sudden pain in the thigh which means a spell on the sidelines.