Dents in race
A sharp dent, like the one shown here, is the result of a heavy blow to the wheel end.

This could be the result of slamming into a pot hole, but it may also be caused by excessive installation pressure.

Multiple dents
Dents in the race caused by external impact loads may progress to spalling of the metal surface. Once the integrity of the surface is broken, wear will progress more rapidly.

This photograph shows where five rollers were driven into the surface of the race. Over time the impacted areas became deeper. With this one, it was probably hard to hear the radio.