AN ACR LTT FLC BUSY WITH AFTER LNDG DUTIES GETS DISTR BY FOREIGN OBJECTS ON TXWY AND CHKLISTS AND HAS A RWY INCURSION AS ANOTHER ACFT WAS PERFORMING A TOUCH-AND-GO.

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UPON TOUCHDOWN AT ATW ON RWY 29; TWR ISSUED INSTRUCTIONS TO 'TAXI R OFF RWY AT TXWY A3; TAXI WITH HER; HOLD SHORT RWY 21.' I READ BACK FULL CLRNC AND REPEATED CLRNC TO CAPT WHEN ACFT WAS SLOWED TO REASONABLE SPD. CAPT REPLIED WITH 'OK.' AS WE TURNED ONTO TXWY A3 WE NOTICED CLUMPS OF MOWED WET GRASS APPROX 1 FT IN DIAMETER; SPREAD ALL OVER THE TXWY. WE NOTIFIED TWR OF THE CONTAMINATED TXWY AND ATTEMPTED TO NEGOTIATE THE ACFT AROUND MOST OF THE CLUMPS TO AVOID SUCKING THEM INTO THE ENGS. UPON CLRING THE CONTAMINATION WE BEGAN THE AFTER LNDG CHKLIST. AS WE APCHED THE HOLD SHORT LINE FOR RWY 21; I WAS STILL READING AND PERFORMING THE AFTER LNDG CHKLIST. AS WE CROSSED THE HOLD SHORT LINE SIMULTANEOUSLY; THE CAPT JAMMED ON THE BRAKES AND THE TWR SHOUTED 'YOU'RE SUPPOSED TO HOLD SHORT.' AS WE ENTERED THE RWY AREA BY 4 FT; A SINGLE ENG ACFT DOING TOUCH-AND-GOES TOOK OFF IN FRONT OF US. THAT ACFT HAD NO TAXI OR LNDG LIGHTS ON. CONTRIBUTING FACTORS: 1) DELIVERY OF A CLRNC DURING A VERY BUSY PHASE OF FLT. 2) FOD ON TXWY THAT DRASTICALLY CHANGED THE NORMAL SEQUENCE OF EVENTS; AND PREVENTED US FROM ACCOMPLISHING THE AFTER LNDG CHK IN A TIMELY FASHION. 3) FATIGUE FROM A +92 HRS MONTHLY SCHEDULE. 4) COMPLACENCY WHERE WE'VE NEVER BEEN ISSUED A HOLD SHORT AT THIS PARTICULAR ARPT BEFORE AND TWR FREQ HAS YOU TAKE CARE OF EVERYTHING -- GND; CLRNC; TWR ON 1 FREQ.