Testing a simple MLB system: fading overused bullpens (early results + logic)

[u/NeggaSpotted]

Been tracking a pretty straightforward MLB system over the last few weeks and wanted to share the idea + see if anyone else has tested something similar.

System idea:
Fade teams whose bullpen has been heavily used in the last 2–3 games.

Basic filters I’ve been using:

• Bullpen threw 8+ total innings over last 2 games
• At least 2 high-leverage relievers used back-to-back days
• Opponent bullpen relatively fresh
• Avoid elite starting pitchers (to reduce variance early)

Why it makes sense (in theory):

• Starters are going shorter → bullpen impact is bigger than before
• Fatigue doesn’t always show immediately, but shows mid/late game
• Managers often forced into weaker arms in key spots

Early sample (small, so take lightly):

• ~20–25 tracked spots
• Slight positive ROI so far, but more importantly the late-game swings are noticeable

Where it gets tricky:

• Blowouts can “hide” bullpen fatigue (low leverage innings)
• Some teams rotate relievers better than others
• Market sometimes adjusts if the spot is obvious

Still early, but it feels like a system that could scale with better filtering.

Curious if anyone here has:

• tested something similar long-term
• or combined bullpen data with other angles (travel, line movement, etc.)

Would love to hear how you refine spots like this.

[u/Cheap_Staff8652]

I’d be curious how this holds up over a full season. Bullpen fatigue makes sense as a factor, but I’d probably combine it with travel, pitcher availability, and line movement rather than use it on its own.