The Green Bay Packers (2-3) may have played the worst second half Sunday since Mike McCarthy became the team's head coach in 2006. Leading 21-3 at the half, McCarthy's Packers allowed 16 points in the third quarter and later surrendered two fourth-quarter leads as the Colts upset Green Bay, 30-27.

The Packers hadn't blown a halftime lead as large as 18 points since 1957, or 55 years.

After re-watching the second-half debacle, here are just some of the things that went terribly wrong over the final 30 minutes:

Turnover spark

The fastest way to jump-start a dead team is giving away the football on your own side of the 50, or exactly what the Packers did on their first offensive possession of the second half. Quarterback Aaron Rodgers said his back-shoulder pass to James Jones was tipped, causing the throw to go to the inside shoulder. Regardless of the process that led to the turnover, an interception was probably the worst-case scenario on the Colts first defensive possession. It gave a flat-lining sideline a heart beat.

Running game goes away

Despite being up 18 points to start the second half, Mike McCarthy waited two possessions and seven plays to finally call a run. Granted, Cedric Benson left in the first half with an ankle injury. But seven straight passes after McCarthy witnessed the offense move up-and-down the field with a balanced play-sheet in the first half? Benson's injury shouldn't have tipped the scales to the passing game the way it did. The Packers ran on nine of 17 plays (53 percent) with Benson in the game, then shifted to 14 out of 44 (35 percent) once he left in the second quarter. When the Packers offense has been one dimensional this season, defenses have teed off on Rodgers. Same story during Sunday's second half in Indianapolis.

Regression up front

After keeping Rodgers clean for eight-straight quarters, the offensive line regressed and Rodgers held the ball too long in the second half. Bryan Bulaga continued a miserable season by getting beat for one of five second-half sacks, but Rodgers was responsible for at least two of the sacks. Marshall Newhouse and T.J. Lang were credited with the other two. The regression is tied directly into the previous point: When McCarthy gets unbalanced with playcalling, defenses gett aggressive in putting Rodgers on the ground. When the run game is present, Rodgers stays clean. It's simple football theory, and the Packers offense in 2012 could be Exhibit A. Sunday was just the latest chapter.

Luck avoids sacks 

Pressure remained on Colts quarterback Andrew Luck throughout the contest, but the productivity in getting him to the ground dried up in the second half. After four first-half sacks, the Packers had none in the second. Several times, and because of several different rushers, Luck was able to escape pressure and find a receiver down field. Luck is a fantastic athlete and a difficult man to bring down, but that lack of finishing on several blitzes and pressures killed the Packers late. Seven-yard losses turned into 12-yard completions, and the Colts offense rolled because of it.

Colts run game gains traction

In the second half, the Colts were down to backups at both guard positions and center along the offensive line. Yet Indianapolis was still able to run the football over the last 30 minutes. On the Colts second possession of the second half, Donald Brown rumbled off gains of nine, 11 and 12 yards as Indianapolis marched down the field. Overall, the Colts ran the football 30 times for 119 yards, but the big chunks came in the second half. That's inexcusable when facing such a ragtag offensive line, even if B.J. Raji did leave in the first half.

Missing turnover opportunities

The Packers defense has lived off turnovers under Dom Capers, but the ball just hasn't bounced their way in 2012. On Sunday, Tramon Williams' inability to intercept an easy pick in the red zone handed the Colts three points. A year ago, Williams probably hangs on to that football and the Packers survive. Credit Casey Hayward for making his play on the football in the fourth quarter, but the Packers need to start cashing in on the opportunities they get defensively.

Missed field goals

Both missed field goals were equally costly. The second kick was obviously the dagger, and Mason Crosby probably won't miss many kicks in his career that badly. Considering Crosby was 5-for-5 on kicks in 2012 and has generally made himself into one of the NFL's most dependable kickers, his two misses were even more shocking. Neither was a gimme, but the Packers expect Crosby to make both, especially indoors.

More officiating mistakes

Sam Shields continues to get flagged for phantom defensive pass interference. Sunday's was awful. How the side official saw anything but perfect coverage from Shields late in the third quarter just goes to show that officials are going to make huge mistakes in these games whether they are real or replacement. And while the call didn't automatically give the Colts seven points, it did turn an upcoming 3rd-and-5 from the Indianapolis' 42-yard line into a 1st-and-10 from the Packers' 17. The Colts were in the end zone four plays later.

Failure to take away the only weapon 

How the Packers failed to neutralize the Colts only true weapon in the passing game is beyond comprehensible. It became clear early on that Luck was looking to Reggie Wayne (13 catches, 212 yards, TD) on every drop back. Yet Dom Capers continued to give Wayne single coverage. There are so many ways that a defensive coordinator can essentially take away a receiver, including bracket coverage where the corner and safety combine to eliminate any throw underneath or over the top. It was done successfully in Week 2 when the Packers took Bears receiver Brandon Marshall out of the contest. Yet for 60 minutes, the Packers failed to adjust to Wayne. Even on the last drive, Wayne caught four passes. Make someone else beat you with the game on the line.