It’s a good photo; shows exactly what’s going on. Typical BW calf’s hair combination rest/strikeplate with the hair worn off on the high point of the rest. I can also see wear on the strikeplate, but not as much. To me, it doesn’t look like wear on the outside of the rest. BW rests are very narrow, and it looks like wear on the normal place the shaft would rub. How long did it take for the hair to rub off? I’m not sure there’s really anything wrong here, although maybe someone will see something I’m not seeing. One thing that could cause this other than just normal wear would be if the shooter is using a split finger grip and is pressing down with his index finger on the nock of the arrow, thus causing excessive pressure on the arrow rest. In this case, the hair would probably be removed while drawing the bow with excessive downward pressure on the arrow nock, rather than when shooting it. The problem is not so much wear on the arrow rest, but the rebound of the arrow away from the shelf when it is shot, which would show a persistent nock high if you were to bare shaft tune, and some loss of accuracy. If he is doing this, the cure is to lower the string elbow a little and make sure that the drawing pressure is straight back, string hand relaxed, without downward forefinger pressure on the nock.