Heading into the 2008 draft, Baseball America concluded their scouting report on Long Beach State right-hander Vance Worley by saying this:

Command is the primary concern with Worley, not in terms of walks but in quality of pitches and efficiency, as he frequently finds himself in deep counts. With refinement of his secondary offerings, he could develop into a mid-rotation starter in pro ball, but his power arm makes a conversion to the bullpen a solid option.

Worley had struggled in his junior season at LBSU, but had impressed enough in the Cape Cod League the summer before that the Phillies ended up selecting him in the third round of that 2008 draft. After a two start stint in the short-season New York Penn League, he finished he season at low-A Lakewood and pitched pretty well, running a 53/7 K/BB ratio in 61 innings. Of course, as a college pitcher facing a string of teenagers, anything less would have been a significant disappointment.

The Phillies moved him up to Double-A in 2009, a more appropriate level of competition for a guy with his experience. This didn’t go so well. He threw 153 mediocre innings, walked 49 batters, struck out just 100, and gave up 17 home runs on the way to posting a 4.39 FIP and 5.34 ERA. His 15.2% strikeout rate was perhaps the most alarming sign, as guys who don’t miss bats in the minors generally don’t make successful conversions as they climb the ladder.

Because of his struggles, the Phillies started him back at Double-A in 2010. At age 22, he wasn’t necessarily behind in his development, but guys are generally expected to show significant improvement if they’re asked to repeat a level, and Worley was only marginally better than he had been the year before. His strikeout rate rose modestly to 17.4% and he got his home run problems under control, but the gains were more incremental than dramatic, and Worley still looked like a guy whose career would probably lead him to the bullpen.

He spent the final two months of 2010 in Triple-A and actually improved with the promotion, as his strikeout rate went up to 19.3% and his walk rate fell to 5.3%. It was an encouraging end to the seaosn, but it was still just 45 innings and he was more good than great, showing stuff that still profiled as more of a back-end starter or a middle reliever.

Worley didn’t rate in any Phillies top 10 prospect list. He was seen as just a guy, a typical minor league pitching prospect with decent stuff but not enough of an out pitch to be an impact big league pitcher. He was a classic fringe prospect, a guy you like having in your system but not someone penciled in as a significant part of the future.

Then, last year, he just got better. He started the year back in Triple-A and posted a 24.8% strikeout rate in 45 innings before getting called up to replace the injured Roy Oswalt. And, despite having only a short track record of getting strikeouts, Worley just kept on rolling in the big leagues. His line for the season – 113 IP, 8.3% BB%, 21.5% K%, 39.3% GB%, 95 xFIP- was quite good for any pitcher, much less a rookie with a spotty minor league track record.

Rather than regression, 2012 has started off even stronger, as Worley’s generating more ground balls (46.9% GB%) and his strikeout rate is as high as it was in Triple-A last year, and ranks as the ninth best mark of any starter with at least 30 innings pitched. His strikeout rate is higher than the one being posted by Justin Verlander, Felix Hernandez, or Clayton Kershaw. His 83 xFIP- ties him with Matt Garza and puts him in between Dan Haren and C.J. Wilson. Seemingly out of nowhere, Worley has been one of the best pitchers in baseball since arriving in Philadelphia a year ago.

Take a look at starting pitchers 24 and under since the start of the 2011 season. Of the 17 arms to throw at least 150 innings over the last seven months, Worley ranks second in ERA (behind only Kershaw), fifth in FIP (tied with Mat Latos), and fifth in xFIP. In a little under one full season worth of innings, Worley has been worth +3.2 WAR, a performance that would make him a borderline all-star in most years.

It’s difficult to ascribe his dramatic improvement to any one thing. He didn’t see any significant spike in velocity, and his fastball still sits 87-93 on most days. He hasn’t added a new breaking ball, nor has he drastically increased his rate of swinging strikes. In fact, Worley has a below average 5.4% swinging strike rate, the lowest total of any of the 17 under-24 pitchers we just looked at, and a number that is the fourth lowest in baseball among starters of any age. Batters make contact with Worley’s pitches more frequently than they make contact on swings at pitches from Bronson Arroyo, Joe Saunders, and Mark Buehrle.

So, what’s the deal? How is Worley racking up so many strikeouts – seemingly out of nowhere – while maintaining his status as a contact pitcher?

The best explanation seems to be deception and location. For whatever reason, opposing batters have only swung at 40.9% of the pitches Worley has thrown as a starter. The only pitcher in baseball to generate fewer swings over the last seven months is Trevor Cahill, but Cahill has had a history of poor command and high walk rates. Worley and C.J. Wilson are the only two pitches in baseball to throw pitches classified as strikes by Pitch F/x more than 50% of the time and see batters swing at them fewer than 43% of the time. The list of low-swing pitchers is almost entirely made up of bad command guys with high walk rates who bury pitches in the ground with regularity, but that doesn’t describe Worley at all.

Worley appears to be throwing pitches that look like they’re headed out of the strike zone, but they rarely actually do. Here’s a heat map of his cut fastballs against right-handers last year, for example:

The yellow areas show the concentration of pitch locations, and you can see that a great majority of them end up on the outer half of the strike zone. Now, here’s the same image, just with his slider instead of his cutter.

While the cutter is more often up and away and the slider is thrown breaking down and away, you can see that they end up in a similar part of the strike zone, and he’s been able to paint the outside corner with his slider. Sliders and cutters can be difficult to distinguish, and if a right-handed batter is reading slider breaking away, but the pitch ends up as a cutter with less horizontal movement, he’ll likely end up starting at a strike.

Worley’s ability to locate his pitches effectively have made him a rare bird indeed – a pitch to contact strikeout machine. In fact, if you look at starting pitchers since 2008, it’s basically impossible to find anyone who sustained this kind of division between their strikeout rate and contact rate over a long period of time. The most extreme examples of strikeouts with contact are Jordan Zimmerman (20.1% K%, 83.4% contact rate) and Cliff Lee (21.4% K%, 83.1% contact rate). The highest strikeout rate by any pitcher with a contact rate over 85% is Kevin Millwood at 15.5%.

At some point, hitters are going to adjust and start swinging at Worley’s pitches more often. It’s essentially impossible to see him sustaining his current strikeout rate without getting batters to swing and miss more often. Of course, he’s already defied most his detractors by pitching so well early in his career, so perhaps he’ll make the necessary adjustments and continue to perform like one of the game’s best starters.

No matter what happens, his career has certainly been unorthodox, and he’s succeeded in a way that few others have ever managed to pull off. What that means for his future is still unclear, but Worley’s story is pretty darn interesting.