Why plant your opposite foot when tossing a ball? If the idea is to get momentum, wouldn’t it make sense to have the foot on the side of your tossing arm propelling forward and not planted? I.e., don’t you want to have added momentum of your body with the toss? Errr…or something…
While we’re at it, or you’re at it, why do we toss a frisbee with the item in the right hand, but we step off with the right hand and the frisbee held on the left side of the body? For overhand toss, that is. For underhand you step with left and toss with right hand with frisbee on right side of the body. Why? ;-|
step of with right hand ← read foot 
You build momentum for throwing by rotating your body around its center of mass, not by thrusting your whole body forward. Swinging your throwing-side leg back while you throw creates a strong rotation with none of the energy wasted by trying to move your center of mass.
If you throw over the same-side foot I think you create a balance problem (I can’t try it at the office at the moment. . . ). It takes energy away from the throw if you have to compensate for a shifting center of mass.
Throwing a ball fast is all about imparting the most velocity into the ball – this comes from energy that you store in your body during the windup. A baseball pitcher is an extreme example of this; they have a very exaggerated windup sequence, starting from lifting the non-throwing side leg, whipping the leg down to a plant, following with body rotation, and finally a whip-like motion of the throwing arm – lots of velocity here, which is why it stresses the throwing arm so much, limiting the number of pitches that can be made without recovery and/or injury.
This same issue is also why a (US) football quarterback can throw so much further/faster when planted in the pocket, rather than when backpedaling – they can get their whole body into the throw rather than just incorporating muscles in the shoulder and throwing arm. For a Frisbee, one usually uses a backhand throwing motion so that the disk spins as well as travels fast, although it is possible to throw sidearm or even overhand; but the most distance usually comes from a big windup and a backhand motion.
FWIW, I used to throw “backwards” due to a groin-pull – I would plant my non-throwing foot and step forwards with my throwing-side leg. It was definitely less efficient.
with a frisbee you can get a similar wind up by spinning around and whipping the frisbee in the usual sideways spin, you spin around 360 and plant your foot while your arm continues the whip around. kinda the same result as a pitcher in baseball.
Well, when I throw a frisbee backhand, I get power by rotating around a vertical axis (left-to-right), as opposed to throwing a baseball, where the axis is horizontal (arm coming over the top towards the bottom). So I start out with my torso twisted way left, then rotate my torso to the right and land on my right foot as I release the frisbee and follow-through.
Of course, throwing a frisbee forehand is completely different, as almost all the energy comes from my wrist (and some from the elbow), and there’s no real torso rotation. Throwing forehand, I tend to step out and to the right, but that’s mostly just to lower my shoulder enough that I can keep a better elbow and wrist angle.
The reason for throwing these ways is that for a frisbee you also need to make it spin as well as push it forward. So you have to find a way that your hand/arm can rotate in the right directions to do so.
This thread seems a little mixed up to me.
Right before the throw, you plant your opposite foot. This allows you to accelerate the throwing half of your body forward to provide maximum speed when you whip your arm forward, and ending with your throwing-side foot planted forward to stop your momentum after the throw.
Yes, and that’s exactly what is happening.
There are two foot plantings here, one right before the throw with the opposite foot and one right after with the throwing foot, maybe that’s where the confusion is coming from.