If, in the judgment of the official scorer, a second player gets an out in what would have otherwise been an error for the first first fielder, the second fielder is credited with an error saved. For example, on April 3rd, 2013, on a ground ball to first baseman Edwin Encarnación,he threw the ball high to the covering Brandon Morrow. Morrow jumped up to receive the ball, then landed in such a way to touch the base in time for the out. If he misses the ball, or misses the bag coming down, Encarnación is no doubt charged with an error. Morrow saved that error, and should be credited as such.
On June 27th, 2015, with a runner on first and nobody out, Matt Boyd pitching. On a comeback grounder to the pitcher, Boyd threw it wide of second base from the covering shortstop José Reyes. Devon Travis, the second baseman, covering the overthrow, threw it back to Reyes for the force out at second. If Travis wasn't backing up the play, Boyd would have been credited with an error. Instead, Travis saved that error, and should be credited as such.