Glossary
Clutch
In one line: Winning a round as your team's last player alive against more than one enemy.
What it means
A clutch situation is when you are the last player on your team and have to win alone against one or more enemies: 1v1, 1v2, 1v3... To "clutch" is to pull it off.
You do not win a clutch by rushing: you win it by tracking the clock, listening for footsteps, fighting one enemy at a time and using the spike as bait. On attack with the spike down, time is on your side; on defense you have to defuse, so you have to act. Calm players win far more clutches than players with the best aim.
An example
Spike planted on A, you are the last attacker against two defenders. You do not go looking for them: you set up on an angle covering the spike and wait. The first one tries to defuse and you take them; the second comes to help and you take them from a different spot. 1v2 won.