There are many myths about throwing and pitching out there. Many of those myths are driven by a lack of understanding; by people's not understanding what pitchers actually do when they throw a pitch.
My hope is that this piece will increase people's knowledge about how pitchers actually throw the ball and decrease the likelihood that coaches will coach their pitchers out of good mechanics and into bad mechanics.
The thing to notice in Frame 154 is that Jeff Suppan is pushing off of the side of the rubber, with the pitching rubber side of his Pitching Arm Side (PAS) foot, through the start of his stride. This helps to establish some linear momentum toward the target which can then be converted into rotational momentum.
As Jeff Suppan continues his hand break, he keeps his shoulders and his hips closed. Notice how, rather than opening his front foot, and thus his hips, he is leading his stride with the side of his Glove Side foot.
While Jeff Suppan does scap load, like Nolan Ryan, Greg Maddux, Randy Johnson, and other durable pitchers, his elbows never get higher than the level of his shoulders. Also notice that Jeff Suppan's hips are just starting to open, and his belt buckle is starting to rotate to face home plate, while his shoulders are still closed.
Based on what Jeff Suppan's Pitching Arm Side foot does as he throws the ball, this is the last frame in which he could be said to be pushing off of the rubber with his PAS foot. From this point on, Jeff Suppan's PAS foot is pulled off of the rubber by the rotation of his hips.
In Frame 178, Jeff Suppan’s Glove Side foot has just planted and his shoulders are just starting to rotate. Notice how his hips are rotating ahead of his shoulders. Also notice how his Pitching Arm Side elbow is just below the level of his shoulders and how he is showing the ball to Third Base, not Center Field.
The rotation of Jeff Suppan's shoulders has caused his Pitching Arm Side upper arm to start externally rotating and his PAS forearm to start laying back toward First Base. Also, in this frame Jeff Suppan has his glove stabilized out over his Gloves Side knee.
The clip below shows that Jeff Suppan finishes in a good, safe fielding position with his glove at his glove side pec, ready to protect both his head and his heart.