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Drysdale has the inverted L, but actually isn't that late at footstrike. You see his arm catches up in the slow motion. Hes a tiny bit late, but negligible. Hes one of those guys who can trick you if you just look at a picture of him right before footstrike (since it looks like an inverted L).
His elbow also isn't elevated. Its right about even with his shoulder line or slightly below.
He also isn't a max effort pitcher, which can be a big part of it as well.