What's wrong with Tom Brady?

New England Patriots quarterback Tom Brady is struggling mightily.

In the wake of a humbling 41-14 loss to the Kansas City Chiefs, Brady's season statistics through four games are ghastly. He's completing fewer than 60 percent of his throws. He's on pace for a career-worst passer rating. He ranks 33rd in the league among 34 qualified QBs in yards per attempt.

Some observers suggest he's in decline. Others point to a substandard offensive line and a dearth of weapons at the skill positions.

We tap our experts to answer the question: What's wrong with Brady?

Sam Monson, Pro Football Focus

In short, Brady is declining. We have seen evidence of it the past few seasons, but it was subtle and slow enough that it wasn't easy to identify. Last season, there were many factors outside of Brady's control that affected his play, and many observers attributed the statistical dip to those other influences. But the fact is we have seen the best of Tom Brady, and the only question remaining is how steep the drop-off will be.

The losses of longtime offensive line coach Dante Scarnecchia and six-time Pro Bowl guard Logan Mankins have been a body blow to the offense. Scarnecchia had been able to craft impressive units year after year regardless of turnover, but this season the New England offensive line has crumbled, abandoning Brady at the very time he needs protection the most. The Patriots have already surrendered 55 total pressures (sacks, hits and hurries), two more than any other team in the league, 25 more than the league average and 45 more than the best mark in the NFL.

It isn't all about protection, though -- Brady's passer rating on 95 unpressured dropbacks this season is just 83.0, and neither of his interceptions came under duress.

Brady is a certain future Hall of Famer, but he can't beat back Father Time forever.

Matt Williamson, ESPN Insider and former NFL scout

Brady is a quickly aging quarterback who has withstood a lot of punishment over his career, and the hits he continues to take are more impactful at age 37.

He is stuck behind a dreadful offensive line that is rotating players at an alarming rate in a desperate attempt to find a combination, any combination, which can pass block. The Pats have yet to find said combination, and Brady is very uncomfortable in the pocket.

He isn't the athlete he once was, either. Never a tremendous physical specimen, Brady's arm strength has waned, and his accuracy has declined.

The Patriots employ no vertical threats in their offense this season. Is that because they don't have anyone to stretch the field, or because Bill Belichick knows that Brady can no longer go deep? There is little speed overall to the offense, and opposing defenses are stacking the middle of the field with defenders.

Steve Young, ESPN analyst and Hall of Fame quarterback

How is it possible with all these draft picks and all this guru stuff we heard coming out, and all the personnel, you know, expertise from the Patriots and how great they've been for so long, that they have not been able to support Tom Brady in his career the past five years, especially this year, with enough personnel to go attack the Super Bowl? How have they fallen so far?

The problem is, people are going to say, 'Oh, Tom Brady is the problem.' He is not. He didn't play well, but I'm telling you there is big separation between what they're trying to do offensively and what Tom wants to do. And also, Tom gets either no help behind the line of scrimmage or no help down the field. Because you saw the tape; nobody's open. In the end, if anybody wants to go after Tom Brady, come through me, because I guarantee you this guy is still capable of taking any team that's really good to the Super Bowl.

Tim Hasselbeck, ESPN analyst and former NFL quarterback

The main problem with the Patriots' offense goes back to the basics of what needs to happen on every pass play: Guys need to get open. That takes time to develop, and Brady and his receivers simply haven't had time this season.

It all starts with the problems up front. We can all sit here and say that Brady has had issues pushing the ball down the field, he's 37 years old, it's over for Tom and the Patriots, etc. But look at the issues on the line, which have ruined the route integrity of pass patterns and forced the Pats to keep an extra guy in to block. You don't have a chance to be successful in that situation.

What's more, they used to have Aaron Hernandez -- who created all kinds of matchup problems -- and they haven't replaced him. They used to have the most dominant tight end in football in Rob Gronkowski; he's still on the roster, but he's not running like he used to. They have a Wes Welker-type receiver in Julian Edelman, but that's the only area where the Pats can say they're not worse off. This is simply not the same team.

John Parolin, ESPN Stats & Info

Tom Brady's 59.1 completion percentage ranks 29th among 36 qualified QBs this season. Among the seven quarterbacks below Brady, only Nick Foles hasn't split playing time.

Brady is missing targets at a much higher rate than in previous seasons. He has misfired on 26 percent of his throws this year, the third-worst mark in the league.

Brady has a 31.8 completion percentage on throws deeper than 10 yards downfield, worst in the league and one of three quarterbacks below 40 percent.

Julian Edelman has been Brady's only reliable receiver. Brady is 25-of-34 when targeting Edelman (73.5 percent), averaging 8.1 yards per attempt with no dropped passes. Brady's completion rate to all other targets is 58.1 percent, averaging 5.5 yards per target with four drops.

Rob Gronkowski has the highest drop percentage of his career (7.4 percent). Brady has connected on 48.1 percent of passes to Gronkowski, who is the only qualified tight end in the league to catch less than 55 percent.

Free-agent acquisition Brandon LaFell has been especially ineffective. Brady has completed 45.5 percent of passes to LaFell -- the fifth-worst mark among 76 wide receivers with at least 20 targets. He has caught a pass on just 12.0 percent of his routes (11th worst).