Doing it with substitutions

sub bowlscore 
 {
   my $t;
   $_=join(',',@_);
   while(s/X,X,X/30,X,X/){}
   s!X,X,(\d)!20+$1.",X,$1"!eg;
   s!X,(\d),(\d)!10+$1+$2.",$1,$2"!eg;
   s!X,\d,/!20,1,/!g;
   s!\d,/,(\d)(\b)!10+$1.",$1$2"!eg;
   s!\d,/(?=,\d\d)!20!g;
   s!(\d\d)(,\d){1,2}$!$1!;
   map($t+=$_,split(/,/));
   $t;
 }
[download]

223 chars not counting the unnecessary whitespace for the body of the function. It's not the lowest bytecount here, but at least it's lower than my bowling highscore.

Update: This fixes a bug pointed out by dragonchild

sub bowlscore 
 {
   my $t;
   $_=join(',',@_);
   while(s/X,X,X/30,X,X/){}
   s!X,X,(\d)!20+$1.",X,$1"!eg;
   s!X,(\d),(\d)!10+$1+$2.",$1,$2"!eg;
   s!X,\d,/!20,0,/!g;
   s!/,X!20!;
   s!\d,/,(\d)(\b)!10+$1.",$1$2"!eg;
   s!\d,/(?=,\d\d)!20!g;
   s!(\d\d)(,\d){1,2}$!$1!;
   map($t+=$_,split(/,/));
   $t;
 }
[download]

10 chars added.

And another correction:
s!\d,/,(\d)(\b)!10+$1.",$1$2"!eg;
should be
while(s!\d,/,(\d)(\b)!10+$1.",$1$2"!eg){}
for multiple spare frames in a row to work.