There is the UD boomerang by itself and then there is the UD boomerang to a UD lasso. The first one is much easier but it is only useful with specific tops, such as double tip tops in which you can throw it so it lands spinning with the upper tip on the hand (I do it in the S8 video). There is one neat trick that you can do with an open top such as a Hollow Point: you catch the top on something like a pencil. I called that trick Pencil Sharpener and did in my worlds 2004 freestyle (you can see it in the Over the Top video). But with a normal top coming at you upside down you have to be able to do a UD lasso and that it is much more difficult.
The way I throw UD is very weird (Jon Gate's words). But it works for me and as far as I know I am the only one doing UD boomerang and UD boomerang to UD lasso. I created the throw with a Spintastics Sidewinder, but it has worked for me for every regular size top that I have tried, from the BK to the Giulia, from the Topdog to the Trompo Grande. I have always suspected that there must be a more "natural" way of doing it, but until somebody else starts doing UD boomerangs using a different throw, I'll stick with mine.
I use the normal wrap and the normal string length. What I do differently is how I grab the top. I hold it horizontally, palm up, but with the string coming on the opposite side of the hand:
This means the top doesn't just roll of the hand but it grinds out (it helps to hold the top close to the finger tips). The tip of the top points to your non-throwing hand.
The throw consists of two very distinct parts. 1) You want to launch the top very smoothly on the way out. The hand is below, so it is a bowling-type throw. 2) At the end of the string you jerk it to come back.
You can tell what part you are messing this way: If it comes standing up instead of UD, you threw too hard. If it comes horizontally, you did not jerk at the end of the string.
I try to get my tops to come back as straight as possible. A little slant of the crown towards you is ok, it doesn't mess up the landing or the lasso.
Practice with a double tip top. After you get it down you can try to UD lasso it, but that is a whole different ball game.
