But before the boo-birds get too worked up, let's stop and consider whether he really deserves the ire.
First, Werth hasn't actually been that bad. He's clearly been unlucky; he has a .263 BABIP, 61 points below his career average. That's a huge aberration.
And despite that, he still has a 93 OPS+, which means he's about 93% as good as the average major league hitter. Now, that's not what you want from your right fielder, but if you normalize the balls in play numbers, his on-base percentage would be right in line with his .361 career average.
The low BABIP doesn't explain his power decline--his ISO power (SLG minus BA) is down to .152 from .236 last year. A ten-point decline could probably explained by leaving the hitter-friendly Citizens Bank Park, but not this. It's still possible that Werth could bounce back this year or next--a 350-AB power drought isn't that usual over the course of a players career. But if Werth finishes the season without ever getting hot, it'll be reasonable to worry.
But the real reason fans feel like Werth isn't meeting expectations is that expectations were unduly raised by his outrageous contract.
Werth had been a good player for about three and a half years in his ages 28-31 seasons. But really he'd only been a quality every day player for the last two full seasons, and it's not unusual for late bloomers like this to fade early. Werth also had big home-away splits in Philadelphia and a long track record of injuries.
Sure, most people figured that Werth would be good for at least a couple seasons and only really become a problem in the out-years of his seven year contract. And some looked at Werth's mix of athleticism, speed, power, defense, and contact ability and saw a guy who could age well.
The point is that casual fans wouldn't be nearly as frustrated with Werth if they hadn't been led to believe that the team was acquiring a perennial superstar. So if you want to boo anyone for Werth's contract, boo Mike Rizzo.
Although I'm not even sure I'd do that yet. Don't get me wrong--I think the Werth contract is one of the worst in baseball. But if he has a bounce-back year next season, and the Strasburg-led Nationals make the playoffs, then it'll be at least in part justified. And we're told that part of the reason that the Nationals made the move was to send a message and change perceptions.
The key question is whether the team is planning on expanding it's payroll over the next 3-4 years and by how much. If the Lerners are prepared to expand payroll to $150 million or more a year like the Phillies and Mets, then the Werth contract won't be crippling. If they intend to stay in the $70-90 range like the Indians or Rockies, then the Werth contract will make it nearly impossible to retain cornerstones like Ryan Zimmerman or compete for free agents in the future.
The true mark of a large-market team isn't so much giving out contracts like Werth's. It's the willingness to eat contracts like Werth's and keep on chugging. It's the ability to make mistakes and move on. The Yankees and Red Sox are full of bad contracts like this. John Lackey. Carl Pavano. J.D. Drew. Kei Igawa. A.J. Burnett. Rafael Soriano. Javy Vazquez. Derek Jeter. Julio Lugo. They survive these deals because they budget for a certain percentage of free agents to become busts, which is what you have to do if you want to play in the free agent market because free agents are by definition older, declining players who cost much more than they can be counted on to produce.
The average NL right fielder this season is hitting .267 / .340 / .438. If you normalized Werth's BABIP, that's basically what his stat line would be now. That's not what the team is paying for, but you can definitely win with that--if you can surround that guy with better players elsewhere. The key question is whether the Nationals are prepared to spend enough to do that. Either way, smart fans won't boo Werth. Blame Rizzo, or don't, but don't blame Jayson Werth for being Jayson Werth.