"loud noise," 1560s, perhaps imitative. Klein compares Gaelic racaid "noise." Meaning "dishonest activity" (1785) is perhaps from racquet, via notion of "game," reinforced by rack-rent "extortionate rent" (1590s), from rack, n.1. But it might as well be an extended sense of "loud noise" by way of "noise or disturbance made to distract a pick-pocket's victim."

"handled paddle or netted bat used in tennis, etc.;" see racquet.