knock on1
1 informal Grow old: she’s knocking on a bit...
- Henning was always a great defender, even when he was knocking on a bit.
- He's a hard-bitten, funny character who admits that he's knocking on.
2 (also knock the ball on) Rugby Illegally drive the ball with the hand or arm towards the opponents' goal line.Chris Spencer drove through the Elland defence but was judged to have knocked on after crossing the line....
- Neil Back escaped with a warning after deliberately knocking the ball on, just out of Burke's penalty reach.
- Rugby is a free flowing game and the play will only stop when somebody knocks the ball on or gives away a penalty.
See parent entry: knock
knock-on2 
noun
1 [usually as modifier] chiefly British A secondary, indirect, or cumulative effect: movements in oil prices have knock-on effects on other fuels...
- The knock-on effect of increased fuel prices may eventually trickle down to everything from the price of milk and a loaf of bread to the clothes we wear.
- Many employees have seen a big drop in remuneration packages during the downturn which has had a knock-on effect on house prices.
- Closing any road is a drastic step, bringing many unwanted and potentially dangerous knock-on effects.
2 Rugby An act of knocking on, for which a penalty or scrum is awarded to the opposition.As well as giving away needless penalties, Scotland could not capitalise on the 26 mistakes made by the Welsh, many of them knock-ons, forward passes and turnovers....
- But, as conditions deteriorated, a drizzle giving way to a steady downpour, so did the standard of play with a succession of knock-ons gifting both sides possession.
- Hennessy and Scott Laird both broke the line on separate occasions but poor passing and knock-ons meant the moves were not completed.