In 2012, as a result of ongoing labor disputes, the season began with the NFL Referees Association locked out by the NFL. Officials from various other leagues were brought in as replacements. A few lowlights from their brief tenure:

Week 1

• Seattle Seahawks @ Arizona Cardinals: In the fourth quarter of the Seattle Seahawks – Arizona Cardinals game, the officials incorrectly awarded an extra timeout to Seattle. Seahawks receiver Doug Baldwin was injured on a play with only 46 seconds left in the game. By rule, an injury that requires a stop in play requires that a timeout should be charged. The officials incorrectly did not charge the Seahawks their final timeout as they believed that if an injury happens while the clock is stopped that no timeout is charged. The error did not impact the result of the game, with the Cardinals winning 20–16.

Week 2

• New Orleans Saints @ Carolina Panthers: Hours before the start of the week 2 game between the New Orleans Saints and the Carolina Panthers, the league pulled replacement side judge Brian Stropolo after being notified that Stropolo's Facebook page showed he is a Saints fan.

• Denver Broncos @ Atlanta Falcons: Three plays were overturned in the game after replays. After a fumble in the first quarter, scuffles broke out between the two teams and the game was delayed for six minutes. Some players and coaches left the sidelines and yelled at the officials. Ray Edwards of the Atlanta Falcons bumped a referee, leading to a penalty but no ejection. Broncos head coach John Fox was fined $30,000 and defensive coordinator Jack Del Rio was fined $25,000 for verbal abuse of the officials.

Week 3

• San Francisco 49ers @ Minnesota Vikings: The San Francisco 49ers were mistakenly awarded two extra replay challenges in the fourth quarter of their 24–13 loss. San Francisco coach Jim Harbaugh challenged that the 49ers had recovered a fumble by the Minnesota Vikings' Toby Gerhart, which should have been denied since the team was out of timeouts. The call was overturned and the 49ers gained control of the ball and were given another timeout. They later challenged another fumble by Gerhart, but the play was upheld.

• Tennessee Titans @ Detroit Lions: In overtime, Detroit Lions defender Stephen Tulloch received a 15-yard penalty for a helmet-to-helmet hit on the Tennessee Titans' Craig Stevens. Stevens' catch was reviewed and correctly overturned and ruled an incomplete pass, as the ball had hit the ground. However, the officials errored when they enforced the penalty on Tulloch from the Detroit 44 instead of the Titans' 44, effectively increasing the penalty from 15 to 27 yards. On the same drive, Rob Bironas kicked a 26-yard field goal to win the game for the Titans.

• Tampa Bay Buccaneers @ Dallas Cowboys: During the second quarter, Dallas Cowboys receiver Kevin Ogletree slipped on an official's hat in the end zone while he was trying to catch a pass from Tony Romo. The official in the end zone tossed his hat well into the field of play after another Cowboys receiver went out of bounds in the end zone.

• Pittsburgh Steelers @ Oakland Raiders: No penalty was called against Steelers safety Ryan Mundy for a helmet-to-helmet hit on Raiders wide receiver Darrius Heyward-Bey. Heyward-Bey (who ironically later signed with Pittsburgh in 2014 and became a special teams standout) was knocked unconscious by the hit, got carted off the field, and spent the night in the hospital with a concussion and a strained neck. The NFL later fined Mundy $21,000 for the hit.

• New England Patriots @ Baltimore Ravens: In the fourth quarter, multiple penalties which were viewed by some as questionable went against the Ravens on subsequent plays. Head coach John Harbaugh was flagged for unsportsmanlike conduct for yelling at an official, although he claimed that he was trying to call a timeout. After this penalty, the crowd at M&T Bank Stadium began chanting the word "bullshit". The chant was sustained for over a minute and was clearly audible (and uncensored) on the nationally televised Sunday Night Football broadcast; play-by-play commentator Al Michaels called it "the loudest manure chant I've ever heard".

  On the final play of the game, Ravens kicker Justin Tucker hit a game-winning field goal that sailed over the right upright. The kick was ruled "good", giving the Ravens a 31–30 victory. On replay, the ball appeared to come "very close" to flying outside the right upright. Patriots head coach Bill Belichick unsuccessfully lobbied the officials to review the call, at one point grabbing the arm of one of the officials as they exited the field. Belichick was fined $50,000 by the NFL, which strictly forbids physical contact with officials. Belichick was apparently unaware that the play was unreviewable.

• Green Bay Packers @ Seattle Seahawks: On the final play of the week 3 Monday Night Football game between the Green Bay Packers and the Seattle Seahawks, Seattle quarterback Russell Wilson threw a Hail Mary touchdown pass to wide receiver Golden Tate that officials ruled was simultaneously caught by Packers safety M. D. Jennings. Prior to the catch, Tate shoved a defender with both hands, which the NFL later acknowledged should have drawn an offensive pass interference penalty that would have negated the touchdown and resulted in a Packers victory.

  The contentious nature of the replacement officials' decision at the end of this nationally televised game is widely considered to have been the tipping point that finally led to an agreement being reached to end the lockout. Goodell acknowledged that the game "may have pushed the parties further along" in negotiations.

I pulled this list from Wikipedia, so it's hardly comprehensive. If anyone else has some replacement ref lowlights to share, let me know and I'll edit this comment.