The reachback prepares speed and line on the backhand: disc straight back, hips turning along, weight behind. With milestones, mistakes and arm protection.
The honest answer: the reachback is the backswing in which you take the disc straight back so it can then accelerate forward on a straight line. A club handout from Graz describes it like this: you take the disc backwards against the throwing direction and turn trunk, head and hips back with it [1]. The centre of gravity moves slightly back, the rear foot is loaded, the front foot unloaded [1].
Why does it pay off? Because spin and distance are linked: in a study with 10 skilled and 11 unskilled throwers, throwing distance correlated with the disc's spin speed in forehand flying-disc throws (r = 0.72 in skilled, r = 0.79 in unskilled) [2]. That is a TRANSFER: it was about forehand throws with flying discs, not the backhand reachback in disc golf.
How hard is it? The backswing is simple; repeating it cleanly takes practice. There is no timeline. The main point first: it isn't about reaching back as far as possible but about keeping the disc on a line on which it can later come forward again. A short, straight reachback beats a long, crooked one.
Both feet stand on a line in the throwing direction (side-on body position), the throwing-hand shoulder points to the target, the arm hangs loose with a slight bend through the whole arm including the wrist [1]. The gaze goes forward to the planned flight path [1].
Milestone: You stand the same way three times in a row without wobbling.
Take the disc backwards against the throwing direction and turn trunk, head and hips back with it [1]. Important: don't take the disc diagonally upward at the back and don't roll the arm in at the elbow [1]. On the contrary, the arm may be extended somewhat again at the back [1].
The centre of gravity moves slightly back, the rear foot carries, the front foot can be slightly unloaded or lifted. The head is turned 90° sideways to almost slightly backward [1].
Milestone: In the side video the disc points roughly opposite to the target at the back and is not tilted upward.
From the reachback you accelerate the disc on a straight line forward, relatively close past the body. The front foot is placed a little forward and loaded, the upper arm and elbow are pulled forward, the trunk rotates as vertically as possible around the spine [1]. Just before release, maximum acceleration with forearm and wrist [1].
The shorter the distance to the basket, the less you reach back [1]. A long reachback for a 20 m throw only brings you errors.
Milestone: You throw 20 m with a shorter reachback as accurately as 40 m with a long one (practice measure).
Practise the reachback without a disc in front of a mirror or window: the Graz handout names details such as "head 90° sideways" and "extend the arm slightly again at the back" [1]. Practised dry, you see every error without the disc distracting you.
The backswing in the backhand in which the disc is taken backwards against the throwing direction while trunk, head and hips turn along [1].
The longer the throw, the further the reachback; the shorter the throw, the less [1]. For a beginner a controlled, short reachback is better than a long, messy one.
Only at the moment of release: on the tee your supporting point must be in the teeing area, before and after you may stand outside [3].
Common causes according to the handout: disc taken diagonally upward, elbow rolled in or looking forward too early [1]. Film yourself from the side and check the way back.
Straddle Putt in Disc Golf: Wide Stance, Straight Line to the Basket