In advance of the rest of a group, doing better than the others. The noun pack has been used for a group of persons since the 1400s, although for about 400 years it had a derogatory connotation, as in “a pack of thieves.” That sense is not implied in the cliché. The act of advancing beyond the others is called breaking out of the pack. A related phrase is ahead of the game, meaning in a position of advantage, usually financial advantage. The game here alludes to gambling, but the term is applied to any endeavor.