"Get your feet on the point!" This is most likely the most shouted imperative over VOIP on Team Fortress 2 when your team is getting pressed back and put on the defensive. And there is a reason for this.

To cap a control point, you have to be standing on it (non-Ubered) and have no enemies present in the control point area. If both teams have players in the control area, the meter will not move. All it takes is one defensive player on the CP to block the meter movement.

This is extremely important on defense, doubly so on Hydro when you only have one CP each, and short routes from map to map where scouts can jump on the CP in a flash. Another situation that this is critical to actually get people on the point is when your back CP unlocks in a 5 point CP map because this CP has such a short timer it can get capped out even underneath a heavy defense.

If your team is down to their last CP (default for Hydro) or defending a specific CP make sure that there is someone physically standing in the point area to block quickcaps, and if there isn't get on the point yourself. Don't fight around the point or try to wait until they get on the point and then hammer them with rockets, or babysit your turrets. Get on the point, at least two or three people. Heavy/Medic pair would be good. Something that will survive for a bit and stop small, fast, leaker attacks. If the rest of your team is on offense they should keep the main force off of your CP. The obvious caveat to this is a Demoman with a full sticky bomb clip on the CP for defense, they need to stay outside suicide range, but they too will need to consider fighting from the point if/when all the other people are wiped off it.

If your team's offensive gets pushed back to the final CP and the entire opposing team is assaulting, keep getting on the CP. It does no good to allow them to move the cap meter uncontested. They will eventually sneak enough people on the point to move the meter to a win, especially on CPs with very short timers. If everyone on your team is in the CP area because you've been pressed there not everyone has to get on the point at once, but make sure you keep an eye on the number of your teammates standing in the CP area and replace them as they die. It is important to keep feet on the point continually, all it takes is one alive player to block a cap attempt, but being tied down to the point is not condusive to life expectancy so replacements will be needed.

Also, if they managed to move the meter any toward the cap it becomes even more important to keep additional people on the point until the cap meter for the CP goes back down to the default value.

This is most important for Heavier classes (Heavy, Soldier, Demo) to keep the point manned. They have a higher life expectancy under fire and are more resistant to insta-gibbing due to higher HPs. Do not let the lone medic hold the control point while the entire team rushes to the next CP. I can't count the number of times this has happened.

If your team is assaulting past you while you're holding down the CP, and you're sitting on the point, don't just join the wave of people, stick to the point unless an adequate defense takes station in your place. One time last night I followed a Heavy (as medic) to the next point because there was a soldier sitting on the point with me providing defense there. What happened? The soldier followed us, and, of course, a scout comes in off the second story, double jumps to the CP, and caps it under the respawn wave's nose. If I had seen that Soldier leave the point I would have doubled back to it, becuase even though a lone medic on the CP is a joke of a defense it is 100% better then nothing at all.

Another thing to consider, is that you should not get bored and wander off the CP if it still unlocked. A scout can come in any time and cap that point, just because they haven't over the past three minutes doesn't mean one won't walk into the room in the next 5 seconds. Some one on your team has to have feet on the point when you're pressed this far back or you will get capped out instantly.

Hopefully people will start to use CP blocking to help retain control of CPs on defense. Until then you'll hear resounding shouts of, "Get your feet on the point!"