This is because normally an x-out ball has low top weight or a real short or long pin length. To the every day house bowlers, these balls will not work properly and the bowler will not like the ball. For this reason the balls are marked X-OUT, but are still sold to the public. The reason that the pro's use them and are allowed to use them is because these balls are still legal according to the USBC and the PBA. As long as the ball is within the regulations with regards to static weights and crap like that, then they can be used. In the last few season when The One was very popular with Tommy Jones and Patrick Allen, both of them used 5 inch pin balls, with the CG down near their thumbs. Its all about getting a certain ball reaction, and anything is legal as long as its static weights fall in the range of legal.
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