Wiktionary
vb. (context ambitransitive rugby English) to commit a foul by knocking the ball forward.
WordNet
n. (rugby) knocking the ball forward while trying to catch it (a foul)
Usage examples of "knock on".
I took the stairs two at a time, and the door marked 3-C opened just as I was reaching to knock on it.
Just as I came round the corner I saw some one knock on the maid's door and go into the cabin.
You knock on the farm- house door and offer two bucks for it, and most likely they're tickled to have you cart it away.
Very early the next morning, there was a knock on my hotel room door.
Two hours later, as Forte was working in his cabin, there came a knock on the door.
The girl used the first audible signal I'd heard since arriving - a very ordinary, though very gentle, knock on a round panel beside the door.