The ScareCrow is one of the more challenging trick catches in freestyle frisbee as it is blind. The position to catch a scare crow is with the arm extended straight and the thumb down. Bend over and twist at the waist so that as you twist you lose sight of the disc. Your arm swings around and you catch it just as you lose sight.
To practice, give yourself a light toss about head height over one shoulder. Toss is either flat of with a slight nose pointing behind you. Then watch the disc, bend and twist and try to find it with the hand opposite of the should you tossed the disc over.
The secret is to watch the disc as long as possible. Turn your head and your eyes toward the disc so that you lose sight only at the last possible moment.
Another tip I forgot to mention in the video is to open your hand as wide as you can. I sometimes will stretch my first finger and thumb to get the opening as wide as possible. This way there’s less chance of the disc hitting your thumb as you come around.