When the San Francisco Giants signed Barry Zito to a 7-year deal worth $126 million in December 2006, I immediately thought of another durable, consistent left-hander that had signed a huge long-term contract several years earlier: Mike Hampton. As it happens, Zito's most comparable pitcher through age 28 according to Baseball-Reference is, shock of shocks, Hampton. Their similarity score is 963, which at the risk of getting too technical, is really freakin' close (1000 represents a perfect match).

Hampton, you may recall, had been a very effective pitcher for the Astros and Mets before breaking the Rockies' bank. He had made 30 or more starts, working at least 210 innings, in each of his previous four seasons. Hampton had been a National League All-Star in 1999 and 2001, had finished among the top five in ERA in 1999 and 2000, was runner up (in an extremely close vote) to Randy Johnson for NL Cy Young in 1999.

Were there warning signs? Sure, but only if you were looking. And, if you were thinking of signing Hampton to big bucks at the time, you probably should have been looking.

The biggest concern was that, despite some sparkling numbers (.670 Win%, 3.30 ERA) from 1997 to 2000, Hampton's peripherals suggested that he might be due for a correction. His WHIP during that period was a pedestrian 1.349; his K/9 (6.10) and K/BB (1.69) similarly underwhelmed. Perhaps most troublesome from the Rockies' standpoint were the total of 200 walks Hampton had issued over the previous two seasons before signing with Colorado in December 2000. If there's one thing you don't want to do at Coors Field, it's put guys on base.

Obviously, PhoneCo Park in San Francisco is more forgiving than Coors Field, but you'd still like to see a front-line pitcher (or at least a guy who is being paid like one) do a decent job of controlling the strike zone. Even at his best, while winning the AL Cy Young in 2002, this was never Zito's strong suit. It didn't matter then, because he was busy dominating hitters. But if you look at his four seasons leading up to the super-mega-deal with San Francisco, you'll see a pitcher who struggled with many of the same issues that made Hampton a risk:

Both were durable and had nice ERAs. The key differences are that Hampton was a year younger, had a shinier winning percentage, and was less prone to the long ball, while Zito did a better job of preventing hits. The numbers that stand out to me, though, are those two on the right: these measure command and ability to throw the ball past batters; neither is what you would expect from "elite" pitchers. They're not terrible numbers, but hint more at middle-of-the-rotation innings eaters than staff aces. They're the type of numbers you'd expect to see from guys like Tony Armas, Doug Davis, Vicente Padilla, or Kip Wells. There's nothing wrong with that, of course; you just don't break the bank trying to procure this sort of talent (unless you're the Rangers and think Padilla's a great pitcher, but I digress).

This is all well and good as an intellectual exercise, but now that Zito's first season wearing orange and black is nearly complete, we need to ask another question: How's that working for the Giants so far? The answer: not quite as well as they'd probably hoped.

Basically, all of Zito's numbers are worse this year than they were over the previous four seasons, which in turn weren't anywhere near the level he'd established back in '02. In other words, not only is Zito no longer the pitcher he was when he was a stud, he might not even be the pitcher he was when he slipped from that exhalted status. He's turning into a right-handed Matt Morris, which is okay if the Giants can swing another sucker deal with Pittsburgh, but it's probably best not to count on that.

One number I added to the previous table was ERA+, which measures a pitcher's ERA against league, taking ballpark factors into consideration. This helps when trying to compare, e.g., a guy who pitches half his games at PhoneCo with a guy who pitches half his games at Coors Field. Here is Zito's line so far this season again, presented with Mike Hampton's first year with the Rockies back in '01:

Sure, there are differences: Zito is tougher to hit and has more success putting the ball past hitters than Hampton did in '01. Neither of these is a huge surprise, though, because that was the case even before both pitchers signed their big contracts. Oh, and Hampton pitched half his games at Coors Field.

Yes, about that. Check out their road numbers:

On balance, things still look better for Zito than they did for Hampton. But is that really a benchmark you want to be using when measuring the success of a big-name, big-money free agent? "Yeah, he's no ace; but he's better than Mike Hampton."

Zito has six years and change remaining on his contract. Given what we know about pitchers, there's a decent chance he'll get hurt at some point. I hope I'm wrong, but the laws of nature suggest that I'm probably not. Zito's list of comparables through age 29 includes several pitchers who had been durable to that point, but who faded quickly: Ramon Martinez, Kevin Appier, Jack McDowell. Even if he remains healthy, Zito's performance this season appears to be reinforcing what the previous four seasons had indicated: that he is much closer to being a mid-rotation starter than an ace.

Acknowledging that no two cases are exactly alike, Hampton's signing should have taught teams a valuable lesson about the dangers of locking up a finesse lefty with declining skills to a long-term deal. The upside of having a slightly better than league average starting pitcher for the next six years wouldn't seem to offset the risk of injury or continued decline. Not at that cost, anyway.

It will be interesting to see where Zito's career goes from here and what lessons future GMs might learn from his case inasmuch as it confirms or dispels what Hampton appears to have taught us.