As above, socks/condoms are preferred.
They must be securely fitted, otherwise it will shoot off
And if brightly coloured it is easily seen to be fitted to reduce the chanches people think you may be in game
Barrel socks were first designed to go on top of plugs as extra security. This can mean some socks were thin and not designed to stop paint, just to hold the plug in place. The quality still varies so if you have a high ROF set then make sure your sock is strong enough in the fabric with reinforcement and the elastic to keep in place and not break in a burst of fire
Plugs can be used if prefered or a sock is not practical
For large barrels such as a flatline, apex or glow attachment do not allow for standard socks.
You either need a jumbo sock or a plug
Plugs can either be just the plug, which is not ideal. Or a plug secured by elastic like a sock. this is vastly better
There is also a plug design with a point on the inside to puncture paintballls reducing their impact
if using a holstered pistol then sock & plug options are reduced to what fits
If the holster has a covered end you could theoretically treat the holster as a sock, but you cannot take it out safely
Some people have holstered the pistol then put on be style of plug with 'wings', this is so they can draw and the plug drops. It still means you cannot take the pistol out safely