Good question. I don't have a degree in agronomy but I think it's because if the turf freezes over night and then it's thawing out in the morning footsteps can do damage. But if it's hard frozen after several days apparently you're good to go.
So... I'm not knowledgeable about this, but I believe we can't play with frost because that damages the grass. Why are sub-freezing rounds allowed? Wouldn't the grass be damaged then too? (And for the record, I'm happy to play in the mid-30s, but not when the wind is more than 20mph.)
Lesson / iron fitting today. I've managed to tame the hook issue and I'm not shoving my right hand over anymore to close the clubface and catch up with my hips/core. Ball flight is on target and my miss is a push that doesn't draw. Still hit an occasional nasty hook, but those are becoming much less frequent. I'm still stuck on AoA of 0.5-2 degrees down, when it was previously more in the range of 2-4 degrees down. My sternum is just hanging slightly back, so working on this is the priority piece for this month.
The timing of this post was perfect for me. I watched the video yesterday, and did an iron fitting with my instructor today. Thanks for the content!
Points 1-3 were pretty well established through conversations with my instructor during lessons leading up to the fitting, as well as email exchanges. I thought I had narrowed down my choices pretty well, but when I arrived and saw all the heads I requested lined up, I realized there was no way I would have time to sufficiently test all of them. We had another good talk and narrowed it down to four (down from maybe ten).
Point 4, I was certainly prepared not to buy anything if the data suggested no improvement, but it was pretty apparent that the shaft/head combos I was testing were noticeably better than my current set.
Point 5, we accomplished this by rotating through the head/shaft combos multiple times, and then throwing out data that were clearly poor swings, and doing multiple passes with different shafts, and switching back to a previous shaft, and basically randomizing the combinations a bit. In the end, we eliminated quite a few shots to get what felt like a representative data set.
The thing that I wasn't prepared for was the physical aspect of the fitting (working from home has taken a toll on my physical fitness). It's been awhile since I've just hit ball after ball after ball like that. When I practice, I might hit 15-20 balls over a period of 45 minutes, with lots of conscious thought and feel rehearsals between each ball. In the end all of the options that I tested performed similarly better than my current set, so I went with the set that I preferred the look and feel/sound of the best.