Lance Lynn, although drawing the ire from some segments of the fanbase for his mannerisms (read: sweat) on the mound, has been nothing but solid in his first two years as a starter. Through his age 26 season, Lance Lynn's 412 ⅓ innings pitched with a 3.82 ERA, 3.34 FIP, and 6.5 fWAR compare favorably with Adam Wainwright's 411 innings pitched, 3.48 ERA, 3.79 FIP and 6.8 fWAR through his age-26 season. Lynn has been successful so far by striking out roughly nine hitters per nine innings. Of the 72 qualifying starting pitchers in 2012 and 2013, Lynn's 9.03 K/9 rate ranks 9th (12th in K%). Keeping Lynn at workhorse status is his poor walk rate. Among those same 72 pitchers in 2012-2013, Lynn's 3.35 BB/9 as a starter is 13th from the bottom. If Lynn can hold those rates steady he will remain a solid starting pitcher, but that has proved to be a difficult task for those who have preceded him.
While Lynn can maintain his walk and strikeout rate and be a very good pitcher, recent history has not been on the side of those who continue to have high walk rates. From 2004-2013, 107 starting pitchers pitched at least 400 innings between the ages of 28-35. Of those, only 34 pitchers had a walk rate above three batters per nine innings and only eight pitchers had both BB/9 above three and an ERA or FIP below four. Many pitchers have had similar starts to Lynn. From 2004-2012, fourteen starters through their age-25 or age-26 season (duplicate names removed) had at least eight strikeouts per nine innings, a BB/9 between three and four and at least 162 innings total from age 27-29 (or 26-28). The group began with a K/9 rate of 8.66. Over the three following years, the rate lowered slightly to 8.37. See the graph below for their performances through age-26 (or 25) season and their following three seasons (In some cases, only one or two seasons were used if the player had not completed those years by the end of 2013).
Despite the potential for survivorship bias (perhaps weighed out by pitchers who pitched in their early 20s being given more chances in their late 20s), the pitchers performed slightly worse over the next three years. Walk rate went down slightly while other statistics were slightly worse. However, as the chart below shows, the averages were weighed down by some very bad performances.
Very few pitchers remained the same in terms of their performance. Of the fourteen pitchers with over eight strikeouts per nine innings and between three and four walks per nine innings, only two, Tim Lincecum and Bud Norris, maintained those rates over the three following years. Lincecum's performance still changed significantly, losing a strikeout and gained more than half a walk per nine innings, while Bud Norris changed his rate stats and kept his results level by losing close to a strikeout and half a walk per nine innings. As the careers of the players in the top half of walk rate compared to the bottom half show, there appears to be an "up or out" pattern among these players. The four players who lowered their BB/9 under three all maintained or improved their strikeout rate, ERA, and FIP. The average ERA and FIP moved from 3.66 and 3.69 to 3.20 and 3.06, respectively. All players whose next three years' walk rates remained over three, even those who lowered their BB/9, got worse over the next three seasons.
Examining only those players with a similar walk rate resulted in similar results. There were twenty-six pitchers with BB/9 between three and 3.5 through their age-26 season who pitched more than 200 innings as starters and pitched more than 162 innings between ages 27 and 29. There was some washout among this group as forty-one players met the initial numbers and fifteen failed to reach 162 innings between ages 27 and 29. The graph below shows average ERA and FIP for the group as a whole, for the group that lowered its BB/9 under three, and the group with a BB/9 rate at three or above.
This group had a lot more room to improve its results, and those that did lower their walk rates showed a much improved ERA and FIP. In theory, Lynn could maintain his high K/9 along with his high BB/9 and remain a solid starter. In practice, pitchers have not often followed that path, either getting better or worse. Lynn has a good chance to continue as a solid starter in the major leagues, but whether you love, hate, or are somewhere in between on the pitcher he is now, he is not likely to be quite the same pitcher over the next three years.