Originally out of Australia, Tanner played high school ball at De La Salle HS in Concord, Calif. A local Bay Area kid, the Giants took Tanner in the third round of the 2006 draft, hoping the six-foot, one-inch lefty would develop over time in the minors. In his first season of professional ball, Tanner was assigned to Short-Season ball, and performed admirably in 13 appearances in relief with Salem-Keizer. He pitched 26 innings and allowed 17 and 10 runs, with 25 strikeouts and only eight walks. His 3.13 K/BB ratio, 3.46 ERA and 0.96 WHIP were all impressive numbers for the 18-year-old in the Northwest League, and his FIP (2.82) and his xERA (1.96) outperformed his ERA, which were good signs in his debut stint.
In his first professional season, he earned a promotion to the Sally, this time as a starting pitcher (as many envisioned he would be when he was drafted). While the strikeouts went down a bit (his K/9 fell to 6.9), he still displayed good control (2.9 BB/9) and command (2.40) over the increased workload (he pitched 135 innings for the Green Jackets). He did prove to be more hittable in the Sally as his H/9 increased to 9.8 and his WHIP jumped to 1.41. However, he did suffer from a bout of bad luck (his BABIP jumped to .335), which explains his 3.19 FIP (though his xERA was 3.93, 33 points higher than his ERA). Nonetheless, at 19 years old and just a year removed from high school, Tanner was a starting pitcher with some upside whom the Giants expected to get better the more he got exposed to professional hitting and developed his secondary pitches.
Going into 2008, there was plenty of attention on Tanner from other baseball analysts. John Sickels ranked him as the 7th best prospect in the Giants system heading into his second full season, grading him as a B- prospect. He didn't disappoint in his promotion in San Jose, as he finished the season with a 10-8 record, a 3.69 ERA and 1.39 WHIP in 117 innings pitched. The strikeouts went down again (his K/9 fell to 6.5), but he allowed less hits in 2008 (his H/9 fell to 9.5), a promising sign considering the Cal League tends to be a hitter's paradise. His FIP in 2008 also improved to 3.08, as did his xERA, which finished at 3.56.
Though he started the year in San Jose again in 2009, the hype was still there for Tanner. Marc Hulet of Fangraphs ranked him as a potential sleeper going into the 2009 season, citing his excellent control and good pitch repertoire which consisted of a high 80's fastball that touched the low 90's, and a slider and curve. Sickels dropped him to No. 12 in his Giants Top-20 list, but he still liked him as a sleeper in 2009, much like Hulet.
Tanner pitched much better in San Jose in 2009, as he benefited from a much more generous BABIP (.289) as well as a better strikeout rate (7.8 K/9) and improved command (2.9 K/BB ratio). He finished his second season in the Cal League with a 12-6 record, 3.17 ERA and 1.25 WHIP in 139 innings of work, a career high at the time. Hulet commended him in his review of the Giants system in 2009 saying this about the lefty:
"Tanner received some consideration for 'The Riser' category before I realized he was listed as the sleeper prospect in the 2008 minor review. The southpaw can be labeled as a soft-tosser, which limits his ceiling to a degree, but the Australian continues to make improvements and have success. Tanner posted a walk rate of just 2.71 BB/9 while repeating high-A ball for the second year."
After a solid campaign in San Jose in 2009, Tanner was ranked as the Giants' 23rd best prospect in Baseball America's Prospect Handbook for 2010. Sickels also ranked him at 16, grading him as a C+ prospect, though noting that he was a borderline C prospect and "that he needed to see if game will work against better hitters" (Sickels noted that he was a bit of a soft tosser that didn't have intimidating stuff).
His first season in the Eastern League though proved to be a reality check for Tanner of sorts. At 23 years old, he didn't blow away guys as easily as he did in the Sally and Cal League. His K/9 fell to a career low 4.8, and he struggled with his command as he sported a K/BB ratio of 1.23. The hit rate also jumped to 9.1, as he allowed 150 hits in 149 IP. While his ERA wasn't bad at 3.68, his WHIP (1.44), FIP (4.44) and xERA (4.04) were a bit disappointing, especially considering his solid 2009 showing in San Jose, and the fact that the Eastern League tends to favor pitchers.
Tanner's stock took a bit of a tumble, as he tumbled to No. 30 in Baseball America's Giants prospect rankings this year, and fell out of John Sickels Top-20 list for 2011. Still despite the regression in Richmond, the Giants still thought somewhat highly of Tanner, as evidenced by naming him to the 40-man roster (though it might have simply been a formality, as he is 24 years old and going into his sixth year of professional ball).
This year, much like his 2009 in San Jose, Tanner has improved in his second go-around in the Eastern League. In six starts and 32 innings pitched, he still proves to be quite hittable (34 hits allowed; 1.44 WHIP), but he has increased his strikeouts (7.1 K/9) and showed better command (2.17). He is not dominating by any stretch of the imagination. That being said, the Giants brass and fans expected some kind of improvement in 2011, and while his ERA (3.94) doesn't suggest it, his FIP (4.20) illustrates that Tanner is figuring it out a little bit better this second time-around in Richmond (his FIP was 4.44 last year).
With a pitching staff loaded with good, young starters at the Major League level, and some promising arms lingering in the minors (Eric Surkamp especially), Tanner doesn't present the promise and upside he once did back in 2008, when he was a sleeper prospect who could be in the Noah Lowry mold. Rob Gordon in his Minor League Baseball Analyst annual for 2011 rated him as a 7C prospect, not exactly disheartening, but evidence that Tanner may not be a slam dunk at the big league level (Gordon rates his potential as a No. 4 starter). Here is what Gordon said in his writeup about Tanner:
"Athletic pitcher with plus slider and fastball location, which compensates for average velocity. Continues to pitch effectively despite a below average FB. Isn't overpowering, but knows how to locate and keep batters off balance. Not a lot of upside, but could see a few seasons as a backend starter."
Considering he's on the 40-man, you would hope as a Giants fan you'd see that potential being realized sooner rather than later. However, with Ryan Vogelsong performing admirably in the absence of Barry Zito, and Zito due to come off the disabled list soon (and you know the Giants are going to pitch him considering how much the Giants are paying him), Tanner seems to be on the outside looking in at this point in terms of breaking into the Majors. The best case scenario for Tanner at this point seems to be a callup to Fresno, and even then, I'm not even sure if the Giants feel Tanner is ready enough to make the jump up to Triple-A.
I still like Tanner for a variety of reasons. I think he has displayed good control over his professional career (he has a career walk rate of 3.1) and good control and command can never be underestimated. That being said, without powering stuff and his tendency to get knocked around by batters, it is safe to say that Tanner's outlook as a prospect is a bit cloudy. It's his sixth season of professional ball, and while has been good at various levels, he has never displayed any real dominance in the minors, and one has to wonder if how that will bode in the Majors (His Minor League Equivalents produced a 4.83 ERA, 1.61 WHIP and 1.00 K/BB ratio based on last year's numbers).
Still, I ranked him at 18 because he is showing some signs of bounce back this year and I think his outlook is still sunny considering his potential. Is he going to be a future front-end starter that's going to pitch 200-plus innings a year? Obviously not. But a back-end starter who could produced decent numbers over 120-150 IP a season in the bigs? I think that's more attainable for Tanner, and not a bad weapon for the Giants to have.