Why UFC 257 will tell us all we need to know about Conor McGregor

MGM GRAND GARDEN Arena was packed with great fighters that night. It was Sept. 27, 2014, and the headline bout of UFC 178 had a championship at stake. The Las Vegas spotlight was also shining on the return of a long-gone former champ. There were even three future titleholders sprinkled throughout the undercard. One of them would soon take over mixed martial arts.

Conor McGregor was stepping into the Octagon for only the fourth time. He had won his first three UFC outings, and he had done so with gusto, intoxicating an expanding fan base with brazenness in his fights and at the microphone. He was a disruptor on the rise, but on this night, he faced a sizable step up the ladder. His opponent…