My son attended four PG showcases. We're obviously PG supporters, or we wouldn't have kept going back.
His ratings bounced all over the place, but there was probably some justification for that.
At his first showcase (the National Underclass), he was an 8. I was pleasantly surprised. Going in, I had expected an 8 or higher, but he didn't perform all that well. He struck out several guys, but also walked several. On the way home, I was speculating to myself that he'd get a 7 or 7.5.
At his second showcase (Sunshine East), he got an 8.5. This was in June, he was in peak shape, and he did great. Unlike the prior showcase, I was a little disappointed. I was hoping for a 9, but that was based partly on the fact that he received an 8 when he didn't perform all that well. But relative to the ratings of other players who attended that showcase, the 8.5 was probably about right.
At his third showcase (SE Top Prospects), his velocity was way off. It was in September and he hadn't been throwing much. His peak velocity was down 4 mph from the prior showcase. Even so, he pitched well -- 3 innings on the mound, great control, and, as I recall, no hits. He got a 7. I had expected a drop to maybe a 7.5 or an 8, but not a 7. But then again, he didn't look all that special tools-wise. I remember watching a Diamond Backs' scout at that event notice my son warming up from a distance. He must have liked what he saw, because he walked over from the field where he had been watching a game just to see my son pitch. He put the gun on him for about 5 pitches. The velocity was nothing special, and so he walked off. (I was crushed). The point is that the DBacks' scout would have probably given my son a "7" that day as well.
My son's final PG event was the World Showcase in early January. He had taken a Christmas trip out of the country and only had one week to get ready (terrible planning on our part). His velocity was only about the same as it had been at the Sunshine East six months earlier (but then again, better than it had been at the SE Top Prospects showcase in September). He performed pretty well against some very high level competition, but given that his velocity hadn't jumped, I was expecting an 8 or 8.5. He got a 9. I guess the reviewer was taking into account the calibre of the batters he faced, as well as the fact that it was the middle of winter. In fact, within a few weeks after that showcase, following his high school baseball conditioning, my son's peak velocity picked up 3 mph from his previous high.
Thus, my guy went from a "7" to a "9" in less than four months. There's some subjectivity involved, as reflected in the different ratings, but the differences also reflect variations in performance. There were times my son came in better condition to play. Looking back, I wish we had skipped the SE Top Prospects showcase. He was not at his best, and the scouts, etc. who come to these events have every right to assume they're seeing a player who has come prepared to display his best.
As for rules of thumb, they're looking to project how players will perform down the road. That involves more than how they play on the particular day of the showcase. Thus, although my guy didn't perform all that well in his first showcase, the PG reviewer obviously saw something in him and liked his basic tools. (As it turns out, he was right -- my son was drafted last week in one of the lower rounds). Likewise, although my son got guys out in his third showcase, his tools (in particular, his velocity) were nothing special. The PG reviewer probably saw a guy who was getting batters out on that particular day, but who could just as easily get knocked around in his next outing.
The bottom line to this long story is this -- whatever rating your son receives, I wouldn't read too much into it. We attended showcases to be seen by the right people and to play against top competition, not to get a rating. The coaches and scouts who are watching your son will give him their own "rating". That's ultimately the only rating that matters.
