The Los Angeles Dodgers, who secured their 7th straight NL West title on Sept. 10, lead the National League with a .654 winning percentage. Their +273 run differential is the highest in the NL by over 100 runs, highlighting their solid balance between quality pitching and hitting. All told, the Dodgers enjoyed another successful season in 2019.

Closer Kenley Jansen, however, is on a two-year downward trend.

The veteran reliever blew a career-high eight saves over the course of the season as his earned run average climbed to an uncharacteristic 3.71. Once an electric, reliable weapon in high-leverage situations, Jansen has recently struggled to find his command and keep hitters off balance.

Jansen closed out the season well, successfully converting a save in each of his last three games.

“I’m very confident,” Jansen said following his most recent save against the Giants. “I just gotta stay focused right now. This is it.”

Jansen, who is 31 years old, entered what is commonly referred to as the decline phase of his career. Every player ages differently, but pitchers typically begin to lose effectiveness in their 30s.

The best evidence of Jansen’s decline can be seen in his average pitch velocity. His cutter, four-seamer and slider velocities have each dropped by approximately 1 1/2 mph since 2017.


Graph by baseballsavant.mlb.com
Graph by baseballsavant.mlb.com


In addition to decreasing pitch velocity, Jansen has also experienced a decline in spin rate on his fastball and cutter.


Graph by basaballsavant.mlb.com
Graph by basaballsavant.mlb.com


Lower velocities and spin rates benefit hitters in a number of ways. Lower velocities mean hitters have more time to determine the pitch’s trajectory, allowing them to remain more selective with their swings.

Lower velocities and spin rates also give the ball more vertical drop, allowing gravity to have a greater influence on the ball’s trajectory. These factors combine to make the ball’s path more predictable to the hitter. Over the past two seasons, each of Jansen’s pitches have exhibited approximately four additional inches of vertical drop.

Graph by baseballsavant.mlb.com
Graph by baseballsavant.mlb.com


As the fastball and cutter drop more, they fall into the hitters’ swing path rather than fly above the barrel. In the modern launch angle revolution, more hitters are swinging at steeper swing planes so as to launch the ball in the air. When pitches drop more, hitters are able to match the ball’s trajectory with their swing plane, resulting in more hard-hit fly balls.

In the past, Jansen’s high velocity and high spin rate allowed his fastball and cutter to play up in the zone and stay above the hitters’ swing plane. However, as Jansen has aged, more of his pitches are finding the barrel of the bat. Fly ball pitchers like Jansen need to be able to stay above the opponents’ barrel in order to induce weak fly balls and strike hitters out.

Not only are batters making more contact on Jansen’s pitches in the zone, but they are making harder contact than before. Jansen’s hard-hit percentage currently sits at a career-high 38.7%, a substantial increase from his career average of 29.9%.

In addition, opponents are pulling the ball at a higher rate than they previously had. Batters typically have more power to the pull side (left field if the batter is right-handed, right field if the batter is left-handed), resulting in more home runs. Jansen used to have great success inducing harmless fly balls; in 2019 however, Jansen’s home run to fly ball ratio was 13.2%, nearly 3 1/2 percentage points above his career mark of 9.8%.


Graph by Fan Graphs
Graph by Fan Graphs


Though his pitches are more hittable in the zone, Jansen is throwing his pitches in the zone at a career-low rate. His zone percentage currently sits at 45.5%, which is more than seven percentage points less than his zone percentage during the 2017 season.

As a result, Jansen’s walk rate has increased to 6.1%, a significant increase from the 2.7% walk rate that he posted in his dominant 2017 campaign. Letting more runners on base and then giving up more hard contact is not a recipe for success.

Overall, Jansen is throwing the ball with less velocity and less spin, resulting in more vertical drop in pitches that shouldn’t be dropping, such as his fastball and cutter. As a result, batters are making more contact and are pulling the ball with more authority than before, resulting in an increased number of home runs given up and a higher average exit velocity. Plus, Jansen is missing the strike zone more often and is giving up more walks, enabling more hitters to reach base more frequently.

Jansen is still capable of being a very good reliever and has shown flashes of greatness this season. Take his recent dominant outing against the Mets, for example, in which he showed excellent command of his pitches, placing them on the corner of the strike zone.

However, when Jansen leaves his hittable pitches in hittable locations, damage tends to be done against him.

Jansen found reasonable success late in the season, compiling a 3.18 earned run average and an excellent 2.42 fielding independent pitching in September. However, his underlying statistics over the last month (a season-low strikeout percentage of 25.5%, a walk rate of 8.5% that is second-highest only to the 11.4% he posted in July, and a season-high expected fielding independent pitching of 4.35) show that he is still far from the dominant force he once was.

And if Jansen fails to regain his former dominance, the Dodgers may have more to worry about than October baseball.