Can the DM interfere with a spell?

Question

Can the DM add in obstacles such as by adding weather, a low class creature accidentally bumping in to the caster, or just a simple acorn falling out of a tree to disrupt a spell?

Answer 1

Yes, heavy weather can interfere with concentration:

Concentration DC1	Distraction
5	Weather is a high wind carrying blinding rain or sleet.
10	Weather is wind-driven hail, dust, or debris.
Distracting spell’s save DC	Weather caused by a spell, such as storm of vengeance.4

1. _{If you are trying to cast, concentrate on, or direct a spell when the distraction occurs, add the level of the spell to the indicated DC.}

4. _{If the spell allows no save, use the save DC it would have if it did allow a save.}

The motion of a ship in a heavy storm can also incur Concentration checks: DC 10 for “Vigorous motion ([...] in a small boat in rough water, belowdecks in a stormtossed ship),” and DC 15 for “Violent motion ([...] in a small boat in rapids, on the deck of a storm-tossed ship).”

Weather conditions are certainly part of the DM’s prerogative as the player in charge of the world and environment. Ideally, of course, weather behaves naturally, and sudden shifts in weather are rare and unusual, or caused magically.

Answer 2

Yes, the DM can interfere with a spell.

The DM controls the environment, the world, and everything that the players encounter. The other players at the table only control what their characters can do within the limits of their role playing and in game capabilities.

From your comment under @KRyan's answer about weather.

Ok thank you that's good, my friend decided to be a sorcerer and I just wanna piss him off coz he thinks he's the best at everything – Jigoku

Should the DM interfere with a spell?

That depends, and gets to the matter of Rule Zero. There are two very thorough answers to that by KRyan and by mxzyplk, both of which provide in depth consideration of when a DM should exercise discretion and act with "the hand of God" -- and when that can be an obstacle to fun at the table.

@KRyan made a comment to your question that I will fold into this answer. (He's very experienced in DnD 3.5e, and I'd consider him an expert witness).

Can the DM do some of these things? Yes. Can the DM do all of these things? Well sooner or later his players are going to get fed up and leave; at that point, he can’t. There is a balance to be struck between challenging players and portraying a realistic, difficult world, and just irritating people.

Sometimes, the DM' "hand of God" alters play constructively. Other times, the DM "hand of God" alters play destructively. Make sure you consider that, and the fun of the players at the table, before you make a "hand of God" decision. Fun is why we play.

Answer 3

Absolutely! However, nerfing the players simply because one can is a jerk move. If the player has the ability to cast a specific spell, and her doing so makes sense in the situation, there's absolutely no reason to interfere with that UNLESS said interference also makes sense. For example, if the DM regularly rolls a percentage die to see if atmospheric conditions are blowing stuff around that could cause the player to lose their action, then yeah, that would make sense. If however he's doing it just to make the encounter more difficult, then he obviously didn't anticipate the player's creative solution, and the DM just needs to eat it and award XP accordingly.

Personally, I love giving extra XP for creative solutions. I feel it encourages the players to connect much more vividly with their world, and it makes them feel like they can actually outsmart the bad guys once in a while instead of simply beating them to death.

If a DM finds themselves messing with the world to make it more favorable to the story they have in their mind, they're doing their job wrong.

The DM's world should be robust enough for the players to do anything they are capable of doing, and the DM should have the ability to react to the players' actions; not the other way around.

Edit: Regarding your friend playing a sorcerer, try putting him in a place where he will be forced to learn discipline and humility. I tend to run high level games nearly exclusively, and with high level players, there's almost nothing they can't magic up, or bash away. As DMs, we tend to think of challenges in terms of high level foes, but what if you had a frail magician who was stranded on an island filled with thousands of primitive warriors, and he could only ask the chief shaman for help? What if the chief lived at the top of a large jungle covered mountain, and the wizard had to traverse the jungle in three days with only a knife, a water skin, and was forbidden from using magic on their sacred land?

There would be no way he could overcome those numbers, and would be forced to undergo a very personal and primal journey, using only his wits and strength to survive. This would force the player to use skills he thought he would never need when he created his optimized character, and would cause the player to grow as well.

These are the kind of challenges I have found DMs tend to not use, but I think that much like today with technology, there are still parts of the world where technology will not help someone, and building that creativity into a world makes it a real adventure at any level.