Piper Flor Begley volunteers to fight but his captain prefers that "Today you'll stride between our lines and martial music play." Tom Barry's fighters defeat 2000 British. "The Piper of Crossbarry, boys, had piped old Ireland free"
[On March 19, 1921], 104 men of the Third West Cork Flying Column of the IRA, under Tom Barry, defeat more than 1000 British and 120 Auxiliaries about 12 miles south-west of Cork city (source: _Tom Barry Leads West Cork Flying Column To Victory at Crossbarry_ at Cork's War of Independence site).
The "Black and Tans" were British reinforcements to regular British soldiers sent to Ireland in 1920. The "Auxiliary Cadets" were veteran British army officers sent to help the Black and Tans. (source: _Michael Collins: A Man Against an Empire_ copyright by and available on the History Net site) For more information see RBW note for "The Bold Black and Tan" - BS
Crossbarry was really two actions: Robert Kee in _Ourselves Alone_, being Volume III of _The Green Flag_ (p. 128) notes that "at Crossbarry... not only did Tom Barry and his flying column successfully ambush a convoy of nine military lorries but fought their way out of a massive attempt to encircle them afterward."
This was not the only victory won by Barry in 1920-1921, nor even his most notorious. He was also, according to _The Oxford Companion to Irish History_, responsible for killing 15 Auxiliaries at Kilmichael on November 28, 1920 -- an event which also inspired a song.
Kee, pp. 120-121, reports of this action, "After a savage fight at close quarters in which three IRA were killed and, according to Barry, the Auxiliaries made use of the notorious 'false surrender' tactics, the entire convoy was wiped out, and seventeen of the eighteen auxiliaries were killed.... [T]he first British officer on the scene... said that although he had seen thousands of men lying dead in the course of the war, he had never before seen such an appalling sight... The doctor at the inquest, an Irishman, said that there was no doubt that some of the injuries had been inflicted after death."
George Dangerfield's history of Irish rebellion, _The Damnable Question_, does not list Kilmichael or Crossbarry but on p. 319 does mention an action of 1920: "On 9 December a flying column under Tom Barry, Commandant of Cork's No. 3 Brigade, and one of the most ruthless and successful of all guerilla leaders, ambushed two lorry loads of Auxiliaries, and wiped them out in circumstances of unusual savagery."
Though the reaction was also ugly, showing how bad conditions were in Ireland at that time: "On 11 December... Auxiliaries and Black and Tans invaded Cork, looting, wrecking, and burning, with the result that the center of the city was destroyed."
Barry would later attack a police barracks in Cork (Kee, p. 128).
Calton Younger, _Ireland's Civil War_, pp. 108-109, notes a case of Barry justifying the murder of a Catholic member of the R. I. C. as he went in to mass, though it doesn't tell whether Barry was actually the assassin.
It's probably no surprise that, when Irish leaders had to decide on the Treaty granting Ireland functional independence, Barry was against it (John A. Murphy, _Ireland in the Twentieth Century_, p. 48).
Tim Pat Coogan (_Michael Collins_, p. 169) sums up Barry and Crossbarry as follows: "Barry in fact was one of the bravest men in the war and probably the most successful field commander.... [H]e achieved a spectacular success at Crossbarry, County Cork, on 19 March 1921. In a day-long engagement, encouraged by the traditional pipes of Flor Begley, Barry and a force of about a hundred men broke through a more heavily armed British encirclement of ten times that number and got away safely...." - RBW
Ironically, Barry (1897-1980) had been in the British Army in Mesopotamia (Kee, p. 70), and had shown no evidence of nationalist sympathies at that time. But he would later become a high officer of the IRA, becoming its Chief of Staff for a time in 1937.
He eventually wrote a memoir, _Guerilla Days in Ireland._