Around the time the battle opened, a detachment of the Prince of Wales' American Regiment (PoWAR) was dispatched northward towards the sound of battle. This contingent seemingly reached the center camp while the fighting was still raging at Bryan's encampment. At the time, the British commander at Hanging Rock, Major John Carden, would not have known that Bryan's men had been completely routed or that McCulloch’s company was in the process of being destroyed. He therefore sent this detachment to Bryan's support, while keeping the remainder of the Provincials in a defensive posture .
At about the time the men of the PoWAR advanced towards Bryan's camp and "passed into a wood between the Tory and centre encampments" , the Americans began their assault on the center camp. Hearing the resulting gunfire, the PoWAR "drew up unperceived" into a line of battle, "and poured in a heavy fire on the militia." The Americans had quickly succeeded in taking the center camp, and at this moment "were forming from the disorder of the pursuit" . Receiving this attack was a band of 30 militiamen . By this "bold and skillful [British] manoeuvre,"  these soldiers were "separated from the main [American] body" still near Bryan's camp . One Samuel Saxon, a company commander, recalled that they turned about and "rushed upon the [British] line and broke our way [through,] losing in killed and missing 15 men" .
The Prince of Wales' American Regiment's Flank Attack (click to enlarge). Saxon's company and others attempt to retreat through the attacking PoWAR. Hanging Rock Creek is at far left. The green patch in the middle distance designates the ravine separating Bryan's camp from the British center camp.
The PoWAR detachment pursued these men towards Bryan's camp, and "nearly changed the fate of the day" . At that moment, however, numbers of Americans led by Thomas Sumter and Robert Irwin were heading towards the center camp, and the attacking British. The Americans were in what appeared to be "an old field,"  when Sumter saw that the British had "found means to turn my right flank" . "The British advanced in good order"  through what appeared to be "a swamp," , or "a marsh" , while the Americans "halted and awaited their approach." Saxon stopped fleeing once he reached this group and "turned about, and took part in the battle which ensued" .
According to one participant:
"The contest was severe and of doubtful issue for some considerable time at length the American troops retreated and occupied a more favorable situation, where undergrowth and brush protected them much from the musketry of the enemy" .
Richard Winn, who was at the center camp, recalled that "On hearing a severe firing to my right I ordered my men to repair to the place." They joined the action "as quick as possible," and came upon "the back of the British" who were "in action" with "a party of our men." Winn gave the order to "commence firing as usual," which caught "the British between two fires." Their line soon "gave way,"  and the Redcoats "took instinctively to the trees and bush heaps," to defend themselves .
Soon "there was not a British officer standing, and many of the regiment had fallen," but still they "returned the fire with deadly effect."  Robert Irwin "had his clothes perforated with four separate balls," but "escaped unhurt" . Richard Winn was not so lucky; he received "a most dangerous wound" .
At last, 22 men, all the rank and file that were left unhurt, "threw down their arms" "on being offered quarters" . Robert Irwin, who had particularly distinguished himself during the fighting  approached an obstinate sergeant major and "wrenched the bayonet" from his hands. Then he too surrendered. 
1. That it was a detachment of the regiment that was sent north, and not the whole regiment, was discussed previously, see Note 1 in this post. The timing of these events is not discussed in participant accounts, but this is the most parsimonious explanation. Several American participants, including Thomas Sumter, asserted that this detachment was sent to Bryan's relief. For Sumter's account, see the letter from Thomas Sumter to Thomas Pinckney, August 9, 1780.
2. William Davie's account; see The Revolutionary War Sketches of William R. Davie [extract]. Davie's account also appears in, John H. Wheeler. (1851). Historical Sketches of North Carolina from 1584 to 1851, Vol. 1.
3. Davie, ibid.
4. The pension application of Samuel Saxon, transcribed by Will Graves.
5. Davie, ibid.
6. Saxon, ibid.
7. Saxon, ibid.
8. Davie, ibid.
9. The pension application of John L. Davies, transcribed by Will Graves. Sumter, ibid., places this event near Bryan's camp.
10. Sumter, ibid.
11. Davies, ibid.
12. Sumter, ibid.
13. Saxon, ibid.
14. Saxon, ibid.
15. Davies, ibid.
17. Davie, ibid.
18. Davie, ibid.
19. Joseph Graham; see William A. Graham (1904). General Joseph Graham and His Papers on North Carolina Revolutionary History.
20. Winn, ibid.
21. Davie, ibid. for the quote; Sumter, ibid., and George Cunningham are the source of the number of surrendered men. For Cunnigham's account, see the pension application of George Cunningham, transcribed by Will Graves.
22. According to Joseph McJunkin, before this battle, he was "called Granny Irwin," but "afterwards [he] was spoken very highly of on account of his good conduct that day." See Will Graves. (2005). What Did Joseph McJunkin Really Saye? Southern Campaigns of the American Revolution, Volume 2, Issue 11.
23. Davies, ibid.