In the big game, you never see the coach take the big shot, or make the big play.
They don't call a time out, bench their starter, and go into the game to make that buzzer-beater three, or kick the game-winning field goal. They leave that up to the players they've coached.
But in sales, you see this all the time - the sales manager stepping in to take the deal into the end zone, or subbing out a salesperson so they can go into a final sales call. This is bad management.
If your sales team isn't strong enough to bring home big deals, the problem isn't with them - it's with you. If you are good manager (or coach), your team is ready for all these situations. They've done enough reps, they've had enough practice, you've given them enough guidance, that they can hit those clutch free throws or make the big sales pitch.
YOUR job is to stand on the sidelines with your clipboard and watch them do what you've trained them to do.