I can't join the forums to ask questions), for example flamethrowing pitchers with good endurance who pitch five shutout innings and then get pulled.
I recently took over a couple teams as well. Did the pitch have 100% fatigue going into the game? If not that might be way. Also he may have thrown a lot of pitches in those 5 innings. Check your manager options as well. It may have been set to pull him at the first signs of trouble.
You see, that's what's confusing. This is his statline from 2 starts ago:
4 IP, 1 H, 2 BB, 9 SO, 28 TB, 50 TS. 78 pitches and the game pulled him!
We won that game 4-1, were leading 3-0 when he got pulled after completing 4 innings. His line for his last start was almost identical. He has no seasonal fatigue (I moved him from closer to starter since he's really rather good) and has EN of 61, admittedly the lowest EN of all my starters.