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The Saber's Edge: Targeting BB% Improvements

Jeff Zimmerman

Zimmerman writes analytics-focused baseball and football articles for RotoWire. He also handles scouting and reporting for and contributes to, and Jeff is also a two time FSWA award winner, including the 2016 Football Writer of the Year award.

Usually, the first stat I look at when comparing pitchers is K%-BB%. It gets to the core of a pitcher's controllable talent. How many batters can they strike out and how few do they walk? The next item I look at is health. How many of High K%/Low BB% innings is the pitcher going to hopefully produce for me? Finally, I look for a high walk rate, the higher the better. Yep, if I have to decide between two otherwise equal pitchers, I will take the walk-happy thrower because walks are one aspect of a pitcher's game that can improve. This week, I will look at why a large walk can be an item to exploit.

Historically, pitchers begin to see a declining strikeout rate as soon as they reach the majors. This decline can be seen in this graph that I helped produce for FanGraphs. Even though some pitchers see an increase, they are definitely the exception. The one aspect of a pitcher's game which historically improves while they age is walk rate. A pitcher typically sees their walk rate decline and stabilize until they turn 29 years old. The average walk age for pitchers who improved their walk rate two percentage points from 2013 to 2014 were 28.2 years old. For those pitchers who saw a walk rate increase, they were 31.0 years old. The reason some fantasy owners like to stay away from pitchers 30-years-old and older, besides health, is their walk and strikeout rates will both be heading the wrong direction. It has been determined pitchers can see a walk rate decrease, but we must remember it should only be used as a tie-breaker.

Let's compare valuing David Price and Madison Bumgarner by using their 2013 stats as a proxy for their 2014 projections. While taking last year's stats is not a good method to project a player, it will work for an example.

Name (age): K%, BB%, K%-BB%
Price (28): 20.4%, 3.7%, 16.8%
Bumgarner (24): 24.8%, 7.7%, 17.1%

Both pitchers should be expected to throw ~200 IP, so they have nearly the same ability. If given the opportunity I would take Bumgarner. Price's near 4% walk rate doesn't have much room for improvement. On the other hand, Bumgarner's rate could drop to 4%...a huge improvement.

So what has the pair done so far in 2014 (besides breaking the norm and seeing their K% jump to 27%). David Price has seen his BB% drop 1.3% points to 2.4% while Bumgarner has seen his drop 2.3% points to 5.4%.

Another reason for going after higher BB% is catching a Cy Young winner in a bottle. In 2009 Clayton Kershaw had a 13% BB%. It was the league's worst rate among qualified starters. In 2013, he was at 6% which is less than half his 2009 mark.

Not all pitchers will find new control, but here are a few under 30-year-old pitchers who have seen a 2% drop in their walk rate from 2013 to 2014 and how they have improved (full list at end of article). I looked at starters only with 20+ starts in 2013 and at least five so far this season.

Name (age) Drop in BB% from 2013 to 2014: Stuff about them

Phil Hughes (28) -3.4%: I am not going to go into detail on Hughes. He hasn't changed much besides his HR/9 numbers regressing towards his career non-Yankee Stadium rate. (I looked at him in detail last week.)

Wei-Yin Chen (28) -3.1%: Chen's chance for any fantasy value will be limited by his 17% K%. Even though the lower walk rate has helped to offset a drop in K%, the K% is just not high enough to add any real fantasy value. Chen is probably only playable in AL-only leagues.

Ian Kennedy (29) -2.9%: Kennedy's lower walk rate (6.2% vs 9.2%) isn't completely unexpected. He had a 6.1% walk rate in both 2011 and 2012. The major change for Kennedy this season is his jump in K% going from 20% to 27%. The main reason for the strikeout increase is a 1.5 mph increase in his fastball. Additionally, he's throwing more pitches in the strike zone, pushing that rate from 43% last season to 49% in 2014. Not surprisingly, a greater number of pitches in the strike zone with increased velocity make a pitcher better (i.e rocket science).

Stephen Strasburg (25) -2.9%: After Tommy John surgery, control is one of the last aspects of a pitcher's game to come back. Strasburg's has finally returned and the rest of the league is paying for it. A BB% near 5% and K% near 30% is insane, especially for a starter. He has made the change by becoming more efficient (3.7 pitches/batter in 2014 vs. 3.9 pitches/batter in 2013), getting a first strike more often (65% vs 60%). The only worry I have with him is avoiding a second Tommy John surgery considering how hard he throws.

Madison Bumgarner (24) -2.2%: Bumgarner has pitched great over the past few seasons and just a few changes have helped improve in 2014. He has gained 0.5 mph on his fastball, and he is getting hitters to swing at more pitches out of the strike zone (career high 32%). The high outside swing rate has helped lead to a career high swinging-strike rate (12%). He is getting more swings at the same time his walk rate is at a career low (5.2%). It will be tough for him to improve much on his current production.

Wily Peralta (25) -2.0%: Peralta will always keep fans interested with his 95 mph fastball. He hasn't yet turned its velocity into an elite level strikeout rate (19% in 2014). The main reason for the low rate is that he is attacking hitters with just two pitches, his slider and fastball. While he does throw a changeup, it is horrible (30% GB% vs. 48% for the league, 11% SwgSt% vs. 15% for the league, 20% HR/FB). Even though he has just the two pitches, he has found a way to be more productive with them. His first-strike percentage is up three percentage points, and he's finding the strike zone more frequently (an increase of four percentage points from last season.) It looks like he is trusting his stuff more and just going after hitters.

Jose Fernandez (21) -2.0% :(

Dallas Keuchel (26) -2.0%: So much goodness going on here. He dropped an ineffective pitch (curve), really decreased another one (four-seamer) and has gone with what works (slider, two-seamer, change). His groundball rate is up 10% points, his HR/9 is one-third of his rate from last season, and his K%-BB% is up from 10% to 16%. During spring training, I always find it interesting to see which pitchers are adding a pitch. In the future, I should probably pay more attention to which pitchers are dropping certain ineffective pitches.