I was playing at a local event yesterday and I was watching a match and one person was attacking with a 3/3, 2/2 , and a 3/4 trample. The other player decides to block the 3/3, and the 2/2, he does not block the 3/4 trample. The player that attack then played Vines of Vastwood after they declared not to block him to give him 4+/4+ to hit them for 7 . The other player said you cannot do that because it was a "Pump" Spell.
Im kinda new to all these rules so whos right in this situation?