In professional sports leagues, "revenue sharing" commonly refers to the distribution of proceeds generated by ticket sales to a given event; the amount of money distributed to a visiting team can significantly impact a team's total revenue, which in turn affects the team's ability to attract (and pay for) talent and resources. In 1981, for example, the Scottish Premier League changed its policy from splitting a match's receipts evenly between its two competing football teams over to a system in which the hosting team could keep all of the proceeds from matches hosted at its facilities. This move is generally believed to have negatively affected the league's parity and enhanced the dominance of Celtic F.C. and Rangers F.C. In contrast, the National Football League distributes television revenue to all teams equally, regardless of team performance or number of viewers. Revenue sharing was a key issue causing the 2012–13 NHL lockout.