LONDON — Coming into these 2017 IAAF world championships, the American Fred Kerley was the next big thing in the men’s 400.

More precisely, Fred Kerley of Texas A&M was the next big thing. He came to London having run 15 individual 400s in 2017. He had won 15.

It didn’t go Kerley’s way in the 400 final. He finished seventh, a result pre-figured in the semifinal, when he just barely qualified for the final on time. This is not to beat on Kerley. Just the opposite. It’s to pay him respect. He’s 22, and — counting the rounds and the final here — he ran 18 400s this year, plus a bunch of relays, plus some 200s to boot.