It was one of the worst games of his NFL career, a three-interception outing in a 27-14 loss to the Green Bay Packers compounded by his horrendous decision to throw across his body into the end zone while trying to hit wide receiver Demetrius Williams.
The pivotal fourth-quarter interception on second down effectively doomed the Ravens' comeback attempt.
Discerning whether there's a direct connection between Flacco's declining health and his sudden regression as a passer over the past five games is complicated.
The nature of how Flacco has gone from one of the top passers in the NFL earlier this season to drop to the 19th-ranked quarterback in the league in terms of passer rating has been accompanied by the second-year pro's issues throwing over the middle and increasing turnovers.
"I think there are a lot of explanations," coach John Harbaugh said. "There are a lot of little things that go play by play. The bottom line is Joe can play better. We can play better around Joe in the passing game. Turnovers are what we're talking about, specifically in the red zone. Those are decision-making errors.
"I'm going to say in the big picture, it's part of his process. Let's get through this right now. Let's make the improvement right now. We try to do that as we go. To win the kinds of games we need to win, you don't turn the ball over generally and you don't turn the ball over in the end zone, for sure. And we've got to get better at that."
During the first seven games of the season, Flacco threw 12 touchdowns with five interceptions for a cumulative 95.9 passer rating.
Over the past five games, Flacco has thrown just two touchdowns with six interceptions for a 69.6 passer rating.
Now, he's coming off a season-worst game for interceptions, passer rating with an unsightly 27.2 mark and his lowest completion percentage, 41.7 percent.
"Obviously this past week, the passing game didn't go too well," Flacco said. "If you look at each game as a whole, I think we've still done what we've been asked to do. We completed most of our passes and, if anything, I just haven't taken care of the ball as good as I should have.
Green Bay, we struggled a little bit, but there were a lot of yards we got from pass interference calls.
"We didn't have very many completions, but that's the way it's going to go most of the time. If you take out the turnover, especially in the red zone, maybe the two turnovers in the red zone, I think we're still in that game and gave ourselves a real shot of winning. We just have to realize that we're headed in the right direction. We just have to keep our head down and make sure we take it one game at a time, and it starts with Detroit."
Flacco sprained his ankle during a loss to the Minnesota Vikings when defensive end Jared Allen stomped on his foot.
He played well against the Vikings and against the Denver Broncos, but began to struggle the following week against the Cincinnati Bengals when he passed for just 186 yards with one touchdown and two interceptions for a 48.3 passer rating.
Is his slide because of the injury and the pounding he has absorbed while being sacked eight times over the past two games?
"As far as throwing interceptions? No," Harbaugh said. "That's part of it. Everybody in this league is nicked-up, but Joe's tough. The thing about Joe is that he is very tough. He's mentally tough, he's physically tough. He fights through it, and that's how it works."
Flacco downplayed the notion that his health is the root cause of his struggles.
Still, it's hard not to notice his body language and his decreased mobility.
"I'm as close to 100 percent as I can be," Flacco said. "I've got bruises and stuff like that, but it's not affecting me out on the field. I didn't feel anything out on Monday night.
"I stood back there and felt great physically. I felt like I was able to move around good, and I'll continue to feel that way as long as our guys continue to do what they're doing."
For the season, Flacco has completed 63.3 percent of his throws for 2,881 yards, 14 touchdowns and 11 interceptions for an 84.6 passer rating.
Flacco acknowledged that defenses are disguising coverage schemes and making adjustments.
It's the Ravens' job to remain unpredictable on offense and take what's given to them as well.
"If you look at some of those game and we would've come out on the better side and won, then nobody would be saying any of this stuff," Flacco said. "The bottom line is we haven't. We haven't done a good enough job, and that's what we'll have to live with."
As a young quarterback, though, there are still going to be growing pains.
Flacco's ill-advised decision to throw across his body and force a play that wasn't there in Green Bay is a prime example of that fact.
"I don't think you ever tell Joe to never, ever, try to make a play," Harbaugh said. "That particular throw, I would say never. I don't think you throw across your body, back to the middle of the field, off your back foot on second down when you've probably got a chance to score a touchdown or, if not, a field goal.
"When you ask him, he will tell you the same thing. But you've got to frame a plan within the offense with the fact that Joe is a playmaker. He's got tremendous ability, and we want him to make plays within the framework of the offense and good decisions."
Following a 3-0 start, the Ravens have lost six of their past nine games.
And the quarterback, fairly or unfairly, traditionally receives the majority of the blame for losses as well as the lion's share of the credit for victories.
"I think it's a combination of everything, all 11 guys," wide receiver Derrick Mason said. "The quarterback doesn't shoulder the blame on every play. If you asked, he'd probably take some of the blame on some of the plays. As a leader and as a quarterback, that's what you do sometimes.
"When we're winning, the quarterback is great. When we're losing, everybody wants to point at the quarterback. It's not the quarterback's fault. It's us as a team."
Running back Ray Rice said he hasn't noticed changes in Flacco's game or demeanor.
"There's no difference in Joe," Rice said. "Obviously teams are playing good football against us. We're shooting ourselves in the foot at times. We won't be saying, ‘Joe's doing any different,' if we're scoring points in the red zone.
"Joe's still playing football. He's trying to make plays for this team, and he's going to continue to try to make plays and make plays."
As the first rookie quarterback in NFL history to win two playoff games and lead his team to the AFC title game, Flacco entered the league with a lot of promise.
Now, he's experiencing a rough spot.
Harbaugh isn't concerned about Flacco, expressing confidence that being tied to the New Jersey native will provide him with a lot of success.
"I don't know if it's fair, but I'm pretty happy about it, to be honest with you, because I think we have a quarterback," Harbaugh said. "As time goes on, he's going to be a tremendous quarterback in this league."
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