knock-on noun 2knock on verb 2forms 4 noun2 •(UK) Resulting as an indirect effect. •A foul in which a player knocks the ball forward, often unintentionally. knock on verb2 •To commit a foul by knocking the ball forward. •(slang) To have an affair; to commit adultery.He's knocking on with her.Those two knocked on together. formsknocked on · knocking on · knocks on · knock-ons