yelling etc
Just before the bell you hear someone yell "Right!". Someone was making a move on the right - if no one on the left accelerated, the left side would have gotten swamped. When you're at the front it's hard to see moves on the opposite side of the field so you need to have tattlers in the field to give you a heads up. I was on the left a few rows from the front and I definitely didn't want to get swamped. So I yelled "Right!". And everyone on the left accelerated
Some organized teams will have one vocal captain who calls out commands to others (which is the correct thing for the leader to do). For example I've gotten leadouts in the past from teammates. One in particular was a full one lap leadout from a guy Chris at this course. On that back stretch, where it's easy to move up on the left, I kept an eye behind us by looking back every couple seconds (Chris was going fast enough that the first 10-15 riders were in single file, perhaps 35 mph at that point). I saw a big group surging on the left - so I yelled to Chris, "Left!". He immediately started moving left (not like a swerve, more like a drift across the road). The 10-15 guys on my wheel moved left also, eating up a lot of pavement - and the surge ran out of room. After the race I saw a friend of mine, asked him how he did. Said that he was too far back at the bell, went with a big surge on the left, then suddenly everyone slammed their brakes on. End of the surge, he was still 30-40 riders back, and end of his race.
When I mention using gaps to move up in the clip - the guy with the disk is in front to my left. He tries to move left and opens a gap which I fill. After I pass the guy with the disk, there's some yelling behind me. Apparently the gap I left (when I moved forward, relative to the field) got filled by two people at once - the guy with the disk and the guy on my wheel. Someone else might have yelled something - you tend to yell if you see two guys about to do something stupid, esp near the end of a race.
You probably heard the "nice save" type yells when the guy bunny hopped into the flowers. You get those too, the complimentary yells.
The grass surfer - guys were telling him to keep pedaling, keep it upright, etc. It wasn't a dumb move, probably a bunch of us would have done the same thing had we been in the same situation, so you tend to forgive what might be considered "not good" by other less hungry and less amp'ed racers. It's a good move if it works and you stay upright. You may notice a lot of hesitation to the grass surfer's left - everyone is waiting to see if "grass surfer" can handle his bike. He can so everyone proceeds.
Sometimes you get the "Hey guys, none of us want to crash, let's take this turn smooth." And when you exit the turn you hear "thanks guys, let's do that at the next turn" lol. It didn't happen here though.
Some of the yelling is simply spectators yelling.
glad you enjoyed,
cdr