Frequency depends on the temp, humidity, and how much you perspire, but you cannot OD on it, so reapply as necessary. I apply liberally in the morning before I leave for the tournament and I keep a bottle in my coaches bucket. The girls also also use it if they get chaffing during the tournament.
My dd prevents chafing to the pitching arm by using the long sleeve under armour. I saw several pitchers in the post season tournaments pitching with the single long sleeve under armour's in hot weather this year.
I carry A & D ointment in every one of my first aid kits. It may be used to prevent chafing if applied to an area where skin rubs against skin on those hot and humitd days. If anyone has had any history with chafing before, they can usually anticipate when chafing may occur and be proactive. A & D ointment works wonders for preventing the chafing from getting worse, once the chafing has started.
Bag Balm works very well for treating chafing problems.
In my younger days, I used to referee 10 to 15 AAU basketball games on the weekends in the summer. Chafing was a constant problem with the referees. Some tournaments, I would referee 6 to 8 games after experiencing some chafing. I would apply the A & D ointment or bag balm and make it through the tournament with minimal pain. My refereeing partners, on the other hand, would run up and down the court bow legged, very painful, but comical to watch.
I never go to a Six Flags park on a Monday after a dd's tournament without A & D ointment in the car. My dd always insists that I go on a Raging Waters ride, log water ride, or whatever water ride is at the park with her. Wet levi's or shorts on a hot day with hours of walking ahead is a chafing incident waiting to occur. Around 6 o'clock at night at the amusement parks, I can tell you with about 90 percent accuracy which poor saps went on the water rides with their kids by the way they walk with their legs spread far apart. I could also be wrong, maybe after 6 o'clock, all the cowboys are arriving to the amusement parks.