Cup Liner
The cup liner is the insert made of plastic or metal that shapes the hole in the green and stabilises its walls.
The cup liner, also called the hole ring or hole insert, sits in the cup and prevents the soil edges from collapsing. By regulation it ends at least 25 millimetres below the surface of the turf, so that a ball lipping in cannot get caught on an edge. Without the liner the hole would wear out after a few flag changes and lose its shape. Most facilities use white plastic inserts to whose lower edge the flag can be fixed.
In practice you notice the cup liner mainly when holing out and during maintenance. An example: your putt runs at pace into the middle, strikes the back wall of the liner and bounces back out. Annoying, but within the rules: the ball never came to rest below the edge of the hole, so it does not count as holed. When the hole is changed, the greenkeepers cut a new recess with a hole cutter, set the liner in place and plug the old hole with the removed piece of turf.
A common error: a ball wedged on the flagstick or against the liner is said to be automatically holed. The only thing that matters is whether part of the ball lies below the edge of the hole and it is being held by the hole. If it is hanging only on the flag above the edge, it still has to be holed — without penalty, by carefully removing the flag. If you are unsure on the green, it is best to clarify the situation together with your playing partners before the ball is moved.
FAQ
What do I do if my ball bounces off the cup liner and springs out?
Then it does not count as holed, even if that is especially annoying. The ball never came to rest below the edge of the hole, so you play it as it lies. A putt hit too hard that strikes the back wall of the liner is a classic example.
Does a ball count as holed if it is wedged between the flag and the cup liner?
Not automatically. The only thing that matters is whether part of the ball lies below the edge of the hole and it is being held by the hole. If it is hanging only on the flag above the edge, you may carefully remove the flag without penalty — if the ball falls in as you do so, it is holed; if it stays on the edge, you have to hole it.
Why does the cup liner sit below the turf?
By regulation the liner ends at least 25 millimetres below the surface, so that a ball lipping in cannot get caught on an exposed edge or be deflected. Without the plastic or metal insert, the hole would also wear out after a few flag changes and lose its shape.