In my PBA experience league I was in the 10th frame and I throw a strike and I walk back and the guy I am bowling gets up and bowls out of turn throws a strike and then walk back completely bowls out of turn because we are bowling like the pros. Then I get up and throw a split and don't convert. He then throws a 9 count and whiffs the 10 pin and I lose by 2 pins man I was mad. The guy running the league said its ok that he did that after trying to explain to me that its in the rules.  I thought that the ball shouldn't of counted. Sorry for ranting!!!

Well I guess this depends on how the league as a whole is accustomed. For instance, in all three leagues I play that would be rather normal, with the exception of when someone's going for a 300 which is a unwritten law.

Cheers
--------------------
-----------------------------------
The best kept bowling secret in Mexico
               Ali

Unless you have something in your by-laws that says one must wait for the opposing bowler to completely finish his frame before bowling his frame, this is completely legal and completely acceptable per USBC rules.  It may not be how people "normally" bowl in your league if you just have an unwritten rule to wait on the other guy, but it's legal and standard practice in somewhere in the neighborhood of 99.9% of leagues.

And if him bowling on his own lane in between your shots in the 10th frame rattled your concentration that badly, you really need to work on your mental game.  Something that minor shouldn't throw you all out of whack!