I agree cabbagedad. To a degree, I think we experienced that with our older one.
It may be as simple as an extension of 'senior-itis' which hits a lot of kids academically.
But it also may be related to perception. Kid has monster junior year, gets scouted/recruited, signs with big school. In the papers. Everyone expect perfection and complete dominance and anything less is perceived as a 'down year' or let down.
To this day, a local HS opposing coach tells a mutual friend that he doesn't think my older son is any good at all and didn't belong in D1...despite the accomplishments he had at that level and beyond.
And then was the experience of our younger son who got bet better his senior year. I will give credit to his HS coach for that one...and maybe a little bit of us not getting all wound up about newspaper articles, etc... and keeping the tone inside the house at a 'business as usual' level all through that senior year. His grades even went up a little!
But its an interesting discussion...and one I hear talked about a lot around the local HS fields.