AN A320 CREW; TAXIING FOR TKOF AT IND; CROSSED THE HOLD SHORT LINE; SPAWNING A TWR INITIATED GAR TO LNDG TFC.

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FLYING AS FO FROM IND TO ORD; ACFT AIRBUS A320. CALLED GND FOR TAXI CLRNC AND GND SAID 'TAXI TO RWY 23L VIA TXWY H; TXWY P.' I READ BACK FULL CLRNC 'TAXI RWY 23L VIA TXWY H; TXWY P.' WE TAXIED TO RWY 23L VIA RTE ASSIGNED AND HELD SHORT OF RWY 23L IN IND. SHORTLY AFTER OUR ARR AT HOLD SHORT POINT; TWR SAID 'ACR X RWY 23R; CLRED FOR TKOF; TURN R HDG 242 DEGS.' FULLY EXPECTING RWY 23L AND THINKING THAT SURELY TWR WAS JUST MIXING THE RWY 23L/R; WE BEGAN TO INCH FORWARD OVER THE HOLD LINE WHILE CONFIRMING 'DO YOU MEAN CLRED FOR TKOF ON RWY 23L; TURN R HDG 22 DEGS?' WE THOUGHT SURELY THIS MUST BE A SIMPLE MISTAKE BECAUSE WE WERE PHYSICALLY RIGHT IN FRONT OF THE TWR THE WHOLE TIME. AFTER QUERYING THE TWR; THERE WAS A MOMENT OF SILENCE AT WHICH POINT TWR SAID 'HOLD SHORT' IN A SLIGHTLY EXCITED TONE; AND CALLED FOR TFC ON ABOUT A 1 1/2 MI FINAL TO GO AROUND. (WE DID NOT SEE SMALL BIZJET.) WE STILL DO NOT KNOW IF THERE WAS CONFUSION ON OUR PART; TWR WAS SIMPLY MISTAKING RWY IDENT WHILE TRYING TO 'FIT US IN' BEFORE THE ARR; OR BOTH. IF WE HAD NOT STOPPED AND PERHAPS IF IT WOULD NOT HAVE BEEN A CLR VFR DAY; THIS COULD HAVE BEEN A DANGEROUS SIT AND A MUCH DIFFERENT OUTCOME!