magic the gathering protection from creatures versus trample

[Josh]

how does protection from creatures work vs trample

[Twanos]

702.17b - The controller of an attacking creature with trample first assigns damage to the creature(s) blocking it. Once all those blocking creatures are assigned lethal damage, any remaining damage is assigned as its controller chooses among those blocking creatures and the player or planeswalker the creature is attacking. When checking for assigned lethal damage, take into account damage already marked on the creature and damage from other creatures that's being assigned during the same combat damage step, but not any abilities or effects that might change the amount of damage that's actually dealt. The attacking creature's controller need not assign lethal damage to all those blocking creatures but in that case can't assign any damage to the player or planeswalker it's attacking. [CompRules 2009/07/08]

Example: A 6/6 green creature with trample is blocked by a 2/2 creature with protection from green. The attacking creature's controller must assign at least 2 damage to the blocker, even though that damage will be prevented by the blocker's protection ability. The attacking creature's controller can divide the rest of the damage as he or she chooses between the blocking creature and the defending player. [CompRules 2009/07/08]

[Josh]

What does this part mean:

" When checking for assigned lethal damage, take into account damage already marked on the creature and damage from other creatures that's being assigned during the same combat damage step, but not any abilities or effects that might change the amount of damage that's actually dealt"

[Twanos]

If a creature has a toughness of 5 and has already taken 3 damage that turn from another source like a lightning bolt for example then you only need to assign 2 more damage to it for it to have been assigned "lethal damage".

Also if the creature with protection is blocking more than 1 creature you count the damage being done to it by the other creatures. For example you have a 2/2, a 3/3 and a 5/5 Trampler all green. You opponet has a creature which protection from green and the ability to block multiple creatures which is 6/6. He blocks all 3 of your guys. Your 2/2 and 3/3 are 5 damage so you trampler only has to assign 1 damage to the blocker and the remaining 4 can trample on over to the player.