Rookies will have bad games. If they occur in isolation, then they can be overlooked. When they form part of a larger picture, then they become significant.
There was a popular narrative among many in the media, and among parts of the fan base, that Glennon had "gotten better with every game", at least until the loss last week to the Panthers. Unfortunately, the game film hasn't borne that narrative out; the truth is, Glennon has been up and down all year. After incremental improvement over his first few games, he took a huge step back in the first game against the Panthers. A better game against the Seahawks was then followed by what was, before today, his worst game as a pro.
And here comes the problem: his worst game as a pro was also his first win. That 'W' overshadowed a lot of issues, but there should be no doubt - the issues were absolutely still there. So when he went on to take a notable step forward against the Falcons, going from his then-worst to his then-best game, a lot of people assumed that it was the continuation of a steady trend of an improvement, rather than a one-game turn around. He followed that up with what was an even better game against the Lions.
That put the streak of consecutive games showing marked improvement at a grand total of two, before the wheels fell off in the second showdown against Carolina last week.
Suffice it to say, anyone who watched today's game knows that it replaced the Miami game as unquestionably his worst offering so far. Not only that, but the nature of the poor play is absolutely cause for real concern.
The statline is a very incomplete story, but it does offer some insight. We know the basic statistics: 90 yards on 9 completions from 25 attempts, leading to a completion rating of just 36% and a yards-per-attempt of just 3.6. His ten-yards-per-completion might sound like a more respectable stat - until you realise that, coming into Week 14, the league's worst yards-per-completion (according to ProFootballReference) is Alex Smith. With 10.5 yards per completion. Two touchdowns and two interceptions meant that his passer rating, for those who care about that sort of thing, was 40.4.
Look beyond the stats, though, and we see a worse picture. Those two touchdowns, Glennon should be given credit for. In fact, I'll say that Glennon's first touchdown drive, which saw him go 4-or-4, was a truly, truly impressive one.
But simple maths should already point out the problem: of his nine completions, four came on one drive. In fact, he managed three completions on his second touchdown drives.
To put it differently: in the other 13 possessions the Bucs had, Mike Glennon had two completions.
It's such an eye-opening stat that I'm going to repeat it: in the thirteen Buccaneer possessions that didn't end with passing touchdowns, Mike Glennon had two completions.
The Buccaneers picked up five first downs through the air all game. That's the second week in a row when the Bucs have had only five passing first downs.
League average? 12.5 passing first downs a game.
Oh, and here's Mike Glennon's stat line for the second half:
Five attempts. One completion. LOSS of 8 yards.
The Bucs won today, because the defense played lights out. The offense was atrocious, and Mike Glennon deserves the lion's share of the blame.
"But wait," I hear you cry, "this offensive line has been playing terribly! The Bills have the most sacks in the league! That has to be taken into account."
It's a fair point. The Bucs do face some very fearsome pass rushes this season. In fact, four of the team's final five opponents - last week's Panthers, today's Bills, Week 16's Rams and Week 17's Saints, came into this week as the four defenses with the highest sack % in the league. That should be a tough ask for any quarterback, let alone a rookie.
Two weeks ago, Detroit got to Mike Glennon a whopping 11 times, in the form of 4 sacks and 7 hits. Last week, the Panthers got the young signal caller 10 times, notching up five of each.
Today, the Bucs' offensive line allowed one sack, and one QB hit. Those two 'QB touches', as I like to call them, represent the least Glennon has been touched all season long.
And with the best pass protection he's had all year, Glennon managed to complete 9 passes, or two completions in 13 of his 15 possessions, or a second half of one-of-five-for-minus-eight.
This isn't a bad game. This is a regression streak that has now matched the longest improvement streak of his short career - two games.
He displayed all the poise of a franchise QB during one drive.
He showed an impressive ability to bounce back with a touchdown drive after throwing two interceptions.
He had a would-be touchdown overturned on what was, by the words in the rulebook, a correct call after review.
And in every other possession he had, he gave no sign whatsoever that he is ready to be automatically named the starter for 2014.