In professional field sports, and especially in collision sports such as rugby league and union, injuries are a somewhat common occurrence in competition and training. The severity of injuries can vary considerably, but those that cause an athlete to miss competitive games are deemed most serious. Other injuries may simply require a modification of training – for example, to reduce or eliminate inappropriate stress/overload for some short period (eg, one day to one week) or specified time (eg, during rehab from a certain injury such as an ACL repair).