Identifying illegal back row attacks

[chartrusepengui]

I switched from card to wheel a couple seasons ago and had a problem. First Varsity Tri I used marker and marked the wheel. It was very hot and humid. Part way into the second set - coach asked for lineup check. I looked at wheel and saw .......... nothing. Everything was gone.

Since then I've stuck to cards. Tried doing both once but still had the problem on hot days. Don't know if it was just heat and humidity or sweaty hand (no ink on hand) or what but I won't ever go back again. I like the card and pencil!