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But Felix' two-seamer breaks down, into the bats.
As well, Dave Allen demonstrated that Felix' two-seamer has armside run, which is right onto the barrel of LH bats (it's a fact that LH hitters rake FB's breaking slightly away from them).
Felix is great, but if he wants to fan hitters, it's the four-seam, non-moving, high-velo fastball that would miss bats...
But the Kevin Brown GB/K paradigm is also kinda okay :- )