Running Amok: The Mariners on the Basepaths

A Mariners-focused look at the new baserunning leaderboards on Baseball Savant.

The team at Baseball Savant released an early holiday present yesterday: the baserunning run value leaderboards! Exciting stuff. Baserunning has always been one of those overlooked ways to generate value on the field, and it often plays a key part in creating marginal advantages that the best teams can use to lead them to victory. But good baserunning isn’t necessarily perfectly correlated with success; of the top 10 best baserunning teams in 2024, exactly half made it to the playoffs and four of the 10 worst baserunning teams played in October as well.

Making things more complicated, baserunning value has always been a bit tricky to quantify. It’s tough to identify good baserunning beyond simple stolen base totals and it’s really easy to point out bad baserunning.

Beyond the eye test, quantifying baserunning value has taken a few forms over the years. FanGraphs uses linear weights and run expectancy to calculate base running value; essentially giving runners credit for positive or negative swings in run expectancy based on how they navigated the bases on any given play. Baseball Savant brought about a new frontier in baserunning analysis when they introduced their sprint speed leaderboards but an all-encompassing value stat was still missing from their ledger until yesterday. Similarly to FanGraphs, they express baserunning value through runs created (or lost).

“For baserunning plays, an estimated success probability is generated for each opportunity using inputs that include runner speed, outfielder throwing arm, runner position on the basepaths and outfielder distance from both the ball and the bases. That can be translated to a run value based on whether the runner successfully takes the extra base, is thrown out or does not attempt to advance.”

Then, they combine the value of a player’s stolen bases and their extra bases taken to create an overall baserunning value. And because they’re leveraging their extensive database, the leaderboard data goes all the way back to 2016.

For the Mariners, Victor Robles appears in the top 5 most valuable baserunners in all of baseball this season. Despite his ill fated attempt to steal home against the Yankees in mid-September, Robles’ aggressive approach on the basepaths led to a ton of baserunning value. Most of that came from his 32 net stolen bases but he also created two runs by taking extra bases. The rule of thumb for runs created is that 10 runs equals one win, which means Robles added nearly a full win to the Mariners ledger through his legs alone.

Dylan Moore and J.P. Crawford generated net positive values with their baserunning while guys like Justin Turner, Cal Raleigh, and Mitch Garver were net negatives. Surprisingly, Julio Rodríguez was net neutral despite stealing 24 bases; the outs he ran into on the basepaths offset all the stolen bases and extra bases gained.

There’s one other avenue of analysis these leaderboards open up: team-level baserunning aggression.

When Jerry Dipoto took over as GM in 2016, he inherited a roster filled with slow, plodding power hitters. As he made his mark on the roster, he identified a number of athletic speedsters to fill key positions — guys like Dee Strange-Gordon, Mallex Smith, and Jarrod Dyson. This shift led to a ton of value created on the basepaths during the lean years of 2018–20. Those teams couldn’t really hit, but man could they run. Things balanced out a bit in ‘21 and ‘22 but a new crop of athletes hit the roster in ‘23 and ‘24. Through it all, the M’s have been one of the most aggressive teams at stealing bases, ranking 8th in the majors in stolen base attempts since 2016.

Despite that aggressive stance on stealing bases, the Mariners have been oddly passive when it comes to taking the extra base. They’re 29th in extra base advance attempts since 2016 and have regularly sat in the bottom 5 in that metric year over year. That kind of passivity when trying to score from second or go first-to-third has hampered their ability to really take advantage of the speedsters on their roster.

Of course, the third base coach throughout this entire nine year stretch has been Manny Acta. I won’t pretend to know how to evaluate the effectiveness of a third base coach — and this data is probably only a small piece of the pie when making that evaluation — but Acta’s role certainly played a part in this team-wide passivity when rounding second or third base. The players obviously play a large role in this baserunning approach as well, though even when the team was filled with speedsters, the number of advancements lagged well behind the value they were actually creating with their legs. From 2018–20, the M’s were the second best team at creating runs via taking the extra base but their attempts rose to just 24th during that period.

Interestingly, Acta’s role has changed for 2025. He’ll be the bench coach for Dan Wilson while the previous first base coach, Kristopher Negrón, will shift over to third. We’ll know pretty quickly if this hesitation to take the extra base was a team-wide philosophy or if it was Acta’s conservative instincts that were holding the runners back.

The other angle that could be at play is the hit suppressing environment of T-Mobile Park. Seattle’s stadium is the hardest ballpark to get a hit in and the dense air of the marine layer causes balls in play to fall earlier than they would in a warmer, drier climate. If it’s simply harder to get a ball in play to fall for a hit, the Mariners would have fewer opportunities to advance an extra base than other teams who play in hitter friendly stadiums.

There’s also the fact that teams often play their outfielders shallower than normal in T-Mobile because they don’t have to worry as much about balls carrying over their heads. Shallower outfield positioning would logically lead to fewer attempts to advance an extra base because the odds of getting thrown out at third or home are higher than normal.

Unfortunately, I have no way to prove either of those theories — the data above can’t be filtered by home/away splits or ballpark. Both of those theories seem sound given the environment the Mariners play in at home. The reality is that it’s probably a combination of all three: park factors, team baserunning philosophy, and coaching decisions. Still, the Mariners need to find better ways to leverage their speedy runners beyond just stealing bases, they need to figure out how to regularly take the extra base and squeeze every little advantage they have out of this roster.