The Ravens, though, are not among those who have questioned his work ethic. Why? The coaches and players saw how prepared Flacco was with the new offense on the first day of offseason workouts.
"Joe is ahead of everybody on the [learning] curve, which he needed to be," offensive coordinator Gary Kubiak said after Tuesday's practice.
It's understandable that Flacco is facing more criticism this offseason. He is coming off a season in which he threw a career-worst 22 interceptions and failed to lead the Ravens to the playoffs for the first time in his career.
But no one should jump to conclusions because Flacco didn't round up his teammates for a couple of practices this spring. He wasn't sitting on some beach for weeks or binge-watching "Orange is the New Black."
Based on what coaches and teammates are saying, Flacco spent time looking at the new playbook on his iPad, learning the different formations and new terminology. The hours that Flacco put in studying in New Jersey benefited him more than tossing passes to Steve Smith at a local high school a couple of months ago.
"I think he worked his tail off when he was away from me," Kubiak said. "The way the rules were set up, we got him as much information as we could so he could study. When it was time to work and get our hands on him, it was obvious how hard he had worked."
Flacco has undergone change in his career. He's on his third offensive coordinator in 18 months. He's working with his sixth quarterbacks coach in his seventh NFL season.
But this is the first time Flacco has found himself in a completely different offensive system. When Jim Caldwell took over for Cam Cameron as offensive coordinator, he didn't overhaul the scheme. Kubiak, however, is installing his version of the West Coast offense.
Not known as someone who expresses a lot of emotion, Flacco has taken a business-like approach in the biggest transition of his NFL career.
"We have a brand new offense, and you can't tell [with Flacco]," wide receiver Torrey Smith said. "The way he goes about it, you can't tell if he's excited about it or if he hates it. That's Joe."
While Flacco has learned the offense, Kubiak has become more familiar with the quarterback as well. When Kubiak was hired in late January, he knew Flacco was a big quarterback with a big arm.
"I had no idea how good of an athlete he is. He's a very good athlete," Kubiak said. "The things we like to do -- move around, the zone pass schemes we like to run -- fit a lot of his strengths, and we need to continue to get better at them. His progress and where he is right now, I couldn't be happier."
Flacco and the Ravens' offense has been a work in progress this offseason. Each week, they have gotten sharper in their execution.
"We're trying to get to the point where we say, 'OK Joe, you got it all, tell me what you feel really good about [the offense],'" Kubiak said. "So, I'm making sure we go out and work on the things that he doesn't feel like he has yet."
Still, no player has a firmer grip on the offense than Flacco right now.
"He's helping put us in the right place," Torrey Smith said. "You can ask him a question, and he always has the answer. That's a credit to him working hard to get it done."