Forum:Vanguard Of The Dragon's effect during battle phase?

I was just duling my brother and I attacked his Vanguard of The Dragon with 1800ATK and he discarded a card thus making Vanguard have 2000ATK. I was wondering if that's a 'legal' move. I didn't think he was allowed to activate his effect at that time. Please tell me if I'm right or if he is. Thanks! Zumax (talk • contribs) 00:24, July 7, 2010 (UTC)Jeremy