During a duel1, my opponent summoned in my field a monster card known as Lava Golem.
When was my turn, I entered in Battle Phase and I go to attack with Lava Golem, but I couldn't.
Here is the description of the card:
Cannot be Normal Summoned/Set. Must first be Special Summoned (from your hand) to your opponent's side of the field by Tributing 2 monsters they control. You cannot Normal Summon/Set the turn you Special Summon this card. During each of your Standby Phases: Take 1000 damage.
I'm wondering, why is not possible attack with Lava Golem. In the linked source and in a quick Google search there's not mention about why such restriction exist in this monster.
1 I was playing the game version known as Yu-Gi-Oh! 5D's Tag Force 5.