B737-300 CAPT OVERSHOT THE RWY HOLD SHORT LINE BTWN PARALLEL RWY AFTER LNDG CAUSING ANOTHER ACFT TO BE SENT AROUND BY TWR.

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AFTER LNDG RWY 28R SFO AND EXITING AT TANGO; ATC INSTRUCTIONS WERE TO HOLD SHORT RWY 28L AT TXWY T. EXITED RWY 28R AND STARTED TO CLEAN UP ACFT AND TAXIED PAST THE HOLD LINE. I WAS 1/2 WAY ACROSS THE LINE BEFORE I NOTICED AND GOT ON THE BRAKES. MY ACFT DID NOT ENTER RWY 28L BUT WAS 1/2 WAY PAST THE HOLD SHORT LINE. ACFT ON APCH TO RWY 28L WAS DIRECTED BY TWR TO GO AROUND. COMMENTS: ALTHOUGH SOME CLEAN-UP OF ACFT IS REQUIRED EVEN BTWN THE RWYS; SUCH AS LNDG LIGHTS OFF; I WAS SETTING THE VOT WHEN I REALIZED I WAS OVER THE LINE. I GOT DISTR FOR A VERY BRIEF PERIOD; BUT LONG ENOUGH TO LOSE SITUATIONAL AWARENESS. IT HAD BEEN A VERY BUSY 1 HR FLT FROM LAS; WITH AN IRS FAULT LIGHT ON DURING CLBOUT; A GPWS TERRAIN OVERRIDE LIGHT; AND A CABIN WRITE-UP. ALSO WE HAD TRIED TO EAT CREW MEALS AND DO SINGLE SEGMENT DISPATCH FOR THE NEXT LEG. I THINK I WAS STILL IN THE 'MULTI TASKING; DO 3 THINGS AT ONCE' MODE AFTER LNDG AND LOST FOCUS ON THE MOST IMPORTANT THING. THE FO AND I DEBRIEFED THIS AND HIS COMMENTS ARE IN LINE WITH MINE. WE BOTH LOST SITUATIONAL AWARENESS.