Swing from the Heels (1912)

They all were swinging from their heels, which fact may account for Baker getting away with only four hits penciled against him.” The San Francisco Examiner, September 8, 1912, p11

Previous earliest use (Dickson Baseball Dictionary, 3rd edition, 2009):
1ST USE. 1928. “The big, burly, powerful chaps, began taking their bat at the end and ‘swinging from the heels’ as the boys say” (George Herman Ruth, Babe Ruth’s Own Book of Baseball, p. 152; Peter Morris).