One defensive back position that is used in certain situations is the nickel back. This player adds extra pass support where needed, and typically comes into the game in the place of the SAM Linebacker. In general, he has the same alignment and assignment as the SAM would. But there are specific reasons that a team will deploy the nickel package.
When Does the Nickel Back Play?
A nickel back goes in when there is a likely pass threat. A team might use more or less of the nickel package in a game where the team they're playing is a dominant pass team. He might also get in the game on 3rd down, or any other game situation where the opposing team is known to pass. He also may be called on to cover a specific wide receiver or tight end that the SAM linebacker isn't as suited to cover.
Who Should Play Nickel Back?
A nickel back has all the skills of a good cornerback. However, he still needs to be a good tackler. In the nickel package, it's a gamble that it's going to be a pass, and you're down a linebacker as part of that gamble. If it turns out that it's a run, the nickel safety will have to step up and take over the run responsibilities of a linebacker.