Is it a good idea to use relievers on back-to-back days?

As fans we see it all the time. Another tight game and the manager makes the walk to the mound to bring in your bullpen’s best pitcher for his second or third consecutive day of work. Either by routine or by role, the manager makes this decision, in most case, purely out of habit without consulting whether the statistics say it’s a good move. But he’s a pitcher the manager has faith in to get the job done.

Every night during the season a situation like this happens. But when you dig into the numbers, it probably shouldn’t be done for the majority of pitchers in baseball.

On the largest sample size–the entirety of Major League Baseball–the concept of using a reliever who pitched the day before puts you at a small disadvantage. The combined ERA of a reliever rises from 3.69 to 3.70 and the WHIP goes from 1.28 to 1.30.

It’s a small difference, but a difference nonetheless. For most teams, that’s maybe a run or two over the course of a season.

But when you consider why a team would use relievers on back-to-back days–close games–those one or two runs may mean the difference between a win and a loss. Between a playoff spot or an October full of tee times.

So maybe my initial argument that the whole league should stop using relievers when they had pitched the day before isn’t totally accurate. But this is something that organizations and managers should be paying attention to on a pitcher-by-pitcher basis.

The Cardinals had the second most appearances of any team by a pitcher who had also pitched the day before last year. The differences in their stats are also larger than the league averages. For Cardinals relievers, the ERA jumped from 2.79 to 2.92 and the WHIP went from 1.23 to 1.39 when using a pitcher who had pitched the day before.

If you compare what that means for the 111 innings that Cardinals relievers pitched after having pitched the day before, and instead substitute the average Cardinal reliever, putting relievers out there on back-to-back days potentially cost the Cardinals 14 runs and an additional 18 base runners late in games.

How many extra wins would 14 runs in close games have given the Cardinals? Enough to clinch the division a few days earlier? Enough to give the guys coming off the DL more time to get their timing back and making them better in October? Perhaps.

For the sake of argument, lets dig into the Cardinals “Big 3.” That’s Kevin Siegrist, Seth Maness, and Trevor Rosenthal. They’ve got some interesting differences of their own.

Seth Maness on 1+ day rest: 4.04 ERA, 1.59 WHIP
Seth Maness on 0 days rest: 4.71 ERA, 1.24 WHIP

Trevor Rosenthal on 1+ day rest: 1.91 ERA, 1.13 WHIP
Trevor Rosenthal on 0 days rest: 2.49 ERA, 1.57 WHIP

Kevin Siegrist on 1+ day rest: 1.53 ERA, 1.07 WHIP
Kevin Siegrist on 0 days rest: 4.50 ERA, 1.50 WHIP

Before I jump in here, if you’ve paid much attention to my writing in the past, WHIP is one of my favorite metrics to analyze relief pitcher performance because of the way runs are charged to relievers. The basic goal of any reliever is to keep guys off base and get outs. WHIP measures that ability. Perhaps better than any other metric.

So when we look at Maness, he was probably a push in 2015, but when you go back and look at his 2014 season, one where he was much better overall, he clearly becomes a pitcher you didn’t want to put out on the mound on back-to-back days.

Meanwhile Rosenthal and Siegrist go from dominant relievers to below average ones overnight. Literally.

So with Rosenthal and Siegrist, you’re talking about pitchers that, when pitching on consecutive days, have a WHIP of 1.57 and 1.50 respectively. Only two Cardinals relievers put up worse numbers last season, Marcus Hatley (2.25) and Mitch Harris (1.59). And neither ever sniffed the mound in the 9th inning of a one run game.

Just comparing statistics, you’re going to find that almost anyone in the bullpen is a better option to take the mound on that second or third day than Rosenthal or Siegrist would be.

The difference would be make up and experience in pressure situations. If you made the decision to pay attention to these statistics, more of your relievers would get opportunities in those types of situations. Some will flourish. Some will faint. Add that information into your decision making.

The Cardinals also develop most of their own talent, so they have the opportunity to get these guys late inning pressure exposure in the minor leagues. That way, when they get to the Majors, they are not unfamiliar with the concept.

Finding a way to better manage these situations is probably the next big advancement in bullpen management. We’re just waiting for the next Tony La Russa to help pave the way.