I did not used to have strong opinions on catching. Unlike throwing, which is a skill that can be taught, I always thought of catching as an art which varied for each player, and each player must find their own way.
As I have done more coaching, and even moreso as I have recovered from hip replacement and watched my skills come back, I no longer think this. Catching can be taught, though of course practice is still a key part.
Thumbs up catchingFor years I have always told people that thumbs-up or thumbs down doesn't really make a difference, you should choose whichever is more comfortable and then do that one consistently. I no longer fully believe that - I now think thumbs-up catching (my way, coincidentally) is better.
I catch thumbs-up to about 8 1/2 feet or even higher. Only for the highest throws do I rotate my arm to get the extra height. I see two benefits of thumbs-up over thumbs-down.
The first is reach. To catch a pass thumbs-down you need to get your thumb underneath the disk. Many is the time where I reached for a distant pass and just hooked a middle finger under the rim, and then pulled it in for the catch. Attempting these thumbs-down, the thumb would not have reached the rim, and they would not have been caught.
The second advantage is the softness of the catch. The hand should have some give to it when the disc arrives, or else it very well could bounce off and end up incomplete. When I catch a disc it does not go to the joint at the base of the thumb, as it would for thumbs-down. Instead I catch it in the middle joint of the fingers, very similar to the way I grip the backhand. This way the hand naturally gives when the disc strikes it, almost delaying the disc in position to be caught.
Of course, the most important thing about catching is the results. If someone is comfortable and successful catching thumbs-down I would never recommend they change what works. But, if I were to design an ideal ultimate player, he (or she) would catch thumbs-up.
FootworkFootwork is, without a doubt, the most important part of catching. Catching is not such an easy thing for the hand to do, so the goal for the receiver should be to make it as easy as possible for the hand. This can be done by providing as close to a standard catching angle and posture as possible.
This means using the feet and legs to position the body so the hand is in a neutral position rather than reaching with the arm. And this means using the proper hand to catch the throw, forehand spin in left hand and backhand in right.
When a hand closes on the disc, the disc still has significant rotational velocity. This can easily cause it to roll out of the hand before the grip is complete, unless an action is performed to keep that from occurring. It is simplest if the spin is always the same direction, as that way the hand only needs to learn a single action to break the spin.
Of course it is not possible that the left hand will always catch forehand spin - there will be the occasional backhand way off to that side where there is not time to set up properly for it. But these should be exceptions, not frequent.
For one handed catching, you do not want to receive the disc directly in front of your body. If you do, the arm is crossing towards the middle, and does not have the freedom to give slightly as the disc arrives. This can cause the disc to bounce out of the hand.
Instead, the arm should be in front at a neutral angle of perhaps 30 degrees from directly ahead. This way the hand is facing forward without flexing the wrist, which can remain relaxed for the catch. The elbow should be straight but not locked, so it can give as the disc is received.
The disc is not caught in the palm, but instead in the lower 2 joints of the fingers, in the same position it is held for a proper backhand. The fingers give a much softer catch than the palm - when the disc hits they give a little, keeping the disc spinning in place rather than rolling out of the hand. If your hand hurts and is bruised after a day of catching you are not doing it right.