It's an attribute in Madden NFL 13, however, and one of the rarest, belonging to only 38 players as the season gets underway. (Others can be made "clutch" through the weekly roster update.) Sure, Eli Manning, Calvin Johnson and Marshawn Lynch are considered "clutch" players, almost by acclamation, but what does that get you in Madden? As the game's ratings czar, Donny Moore, explained it to ESPN:
• If a team trails by 8 or fewer points, or is tied, in the final two minutes of regulation or in overtime, the clutch trait kicks in.
• Clutch quarterbacks see an attribute boost for themselves and all of the offensive line.
• Clutch running backs, receivers and tight ends get a boost only for themselves.
• Clutch kickers see a boost in accuracy and power, but the margin must be 3 points or fewer in the final two minutes of the game. The boost also kicks in only if it's fourth down, unless it's under 10 seconds left in the game.
• On defense, clutch only matters for defensive backs and linebackers, and their side must be within one possession, winning or losing, in the final two minutes or overtime.
• Clutch does not affect punting. There are no clutch punters. God, why would you suggest such a thing
How'd they decide who was clutch? Well, Moore used the test Justice Potter Stewart famously applied to porn. He knows it when he sees it.
As for the attribute boosts, quarterbacks get increased ball carrying, play action, throw accuracy and throw-on-run attributes, plus awareness, which means basically nothing if you are controlling the quarterback. The offensive line gets a "MAJOR" boost to pass blocking, so think about that as you decide whether or not to mix in a run.
Running backs get boosts to ball carrying and catching, plus pass block and stamina; receivers and tight end get boosts to spectacular catch, catching, catch in traffic—you get the idea. For more on what gets goosed and who gets it thanks to being "clutch," see the link.