From a physics perspective, what happens when someone goes bungee jumping is remarkably similar to the stretching that should happen on an anchor in WCS, according to Robert Royston.
Let’s say that you have a bungee cord that is 20 feet long, and you jump off a bridge. For the first 20 feet down, you are in a free-fall. At 20 feet, your speed begins to slow as the bungee cord comes under tension, but you are still moving towards the ground. You fall slower and slower as the bungee cord reaches its maximum stretch, at which point the bungee cord begins to recoil and you are pulled upwards. In physics terms, there is an arc of momentum for the bungee jumper: the momentum slows as the bungee cord reaches maximum extension, pauses for a split second, and then builds in the other direction as the cord pulls back.
The experience of stretching the cord and slowing your speed until the moment right before recoil is the experience that we want to replicate in the anchor of west coast swing. When done correctly, the leader and follower will both feel that natural maximum stretch that makes the follower want to recoil (i.e., come forward), and the leader will know exactly when the follower is in that moment of maximum stretch.
The Drill: To practice stretching and becoming aware of this arc of momentum, find a partner and stand a little more than an arm’s length apart. You want to be able to connect in an anchor position and have some tension without causing either partner to be fully extended or to lose frame. Place your feet in an anchor position, with the leader’s weight on the left and follower’s weight on the right (like the & count of the anchor). The follower should slowly roll onto her left foot, making sure to move her center back as she rolls towards the heel. The leader should roll into his right foot as he feels the follower doing so, with the goal of matching her speed.
As both partners settle into their heels, the leader should feel the stretch building until it feels natural to redirect the follower forward. This is the point at which the leader should step back (with a body lead). Both partners can stop moving after stepping the 1 of the next move and reset. The transition between the anchor and the next move should feel fluid. If the leader led too early, the follower will feel jerked out of her anchor. If the leader led too late, the follower will feel like her momentum has died and it requires effort to come forward on the 1; the follower may also feel overextended or break frame if she is allowed to settle back too long.
Bonus Variations: You can extend this drill by practicing having the follower roll back onto the heel at different speeds. You can also have the follower turn the stretch into a hitch by not reaching the moment of maximum extension until 1; in that case, the leader should lead a blank-&2 rhythm (e.g., hold ball-change) instead of the normal walk-walk for the next pattern.