The awkward sequence came with 4:14 remaining in the Steelers' 31-28 loss on Sunday at the Mercedes-Benz Superdome in New Orleans.
The Steelers led the Saints 28-24 when punter Jordan Berry came onto the field for a punt on a 4th-and-5 from their own 42-yard-line. Pittsburgh snapped the ball, but instead of going to Berry the ball went to Nix.
The 5-foot-11, 248-pound fullback sprinted through the line of scrimmage before being brought down by three Saints defenders. Nix -- who was obviously short of the first down -- jumped up and high-stepped over midfield before going to one knee and holding the ball up to signal a first down.
But the Saints were also celebrating. Several other Steelers players joined Nix in his erroneous joy before the Saints took over on downs.
"I just wanted to be aggressive," Steelers coach Mike Tomlin told reporters. "I wanted to insure that we had an opportunity to win the game. I liked the play, the concept. I thought we had a chance to get it."
The four-yard gain was Nix's only carry in the contest and first of the season. Jaylen Samuels paced the Steelers' rushing attack with 53 yards on 12 carries. Nix had three carries last year and now has four total carries during his four-year NFL career. The Kent State product made the Pro Bowl last season.
The Steelers host the Cincinnati Bengals in the last game of the regular season at 4:25 p.m. on Sunday at Heinz Field in Pittsburgh.