You can stop your opponents from capturing a point, or pushing a payload cart by simply standing on or near it. Any class near the point should at least make an effort to stall point captures if either team is close to victory. If your opponents have almost captured the last control point, or there’s just a few seconds left on the clock, a lone Engineer leaving from his sentry nest to block his opponents from capturing could give his team the two seconds they need for the power classes to respawn or get to the cart and push the other team back.
Bonus Tip: Standing on a capture point your opponents have capture time on will revert their progress. Do this when a Attack/ Defense game goes into overtime, or when you’re about to leave and capture your opponents points in 5 CP games.