Being an MLB closer may be the toughest job in baseball. Typically, a closer is tasked with preserving a tight lead in just one inning, after sitting for the first eight innings of a game. There is very little room for error, but the potential for a mishap is very real.
There are several closers in baseball who have the ultimate job security. Either they are among today's elite stoppers—such as the New York Yankees' Mariano Rivera or the Atlanta Braves' Craig Kimbrel—or their club simply has no better alternative on the roster.
But there are also closers who should be looking over their shoulders, as their job security is growing very thin. This could be a result of a number of extenuating circumstances—such as poor performance—or it could be due to a team's regular closer returning from an injury. Regardless, the following pitchers shouldn't get too comfortable in the closer's role, as they may have a new assignment soon.
*Note: Carlos Marmol of the Chicago Cubs has already lost his job as the team's closer, and thus, does not qualify for this list.