There are two considerations: RAW and Narrative. Which applies, depends on the nature of the block and the nature of the character following.
Block: Roll to set up a preemptive defense against a specified future action; anyone committing that named action will have to roll against the block to succeed
So, one would assume that the wizard made a block against someone moving from zone to zone. But, in my group, we wouldn't let such a declaration stand. It would have to be something that was appropriate to the situation and the wizard. If it were a wizard of air in an alley, he might say he uses his (insert name of spell/rote) to summon a gust of wind and drop the crates that are stacked precariously to prevent being followed.
So we go a bit further to YS210:
To perform a block, declare what specific type of action the block is intended to prevent and roll an appropriate skill. The total of that roll is called the block strength. During the exchange, any time a character wants to perform the action that’s covered by the block, he must roll against the block and meet or exceed the block strength to be able to perform that action. If he fails, he
cannot perform the action in question. If he meets or exceeds the block strength, the action resolves normally, with benefits for extra shifts if
the roll beats the block strength by a wide margin.
This would tend to lead towards no matter what you do, you have to overcome the block. But the next part about resolving blocks clears that up a bit. On the same page in Your Story under Resolving Blocks:
Sometimes blocks are a little trickier to resolve than other actions because they seek to prevent an effect rather than create one. When you create a block, the block has to be specific and clear in two ways: who it’s intended to affect, and what types of action (attack, block, maneuver, move) it’s trying to prevent. Generally speaking, if the block can affect more than one person, it can only prevent one type of action. If the block only affects one person, it can prevent several types of action—up to all of them—as context permits.
So looking at this block and the way it's narrated, it's a block against anyone that tries to get through the stack of crates. That's still very hard to resolve- the rules say one type of action. But an opposing character could use a variety of ways to contravene the block. Parkour up the stack of crates. An opposing wind blast to clear the way. Mighty strength to power through. Would it apply to each, and how? And what about the case of the person with Mighty Strength leaping over the whole obstacle? Or someone that flies?
If the obstacle directly opposes someone's action, I think that the action has to be assessed to see how it interacts with the narrative of the block.
If the narrative of the block doesn't interfere with the action being proposed- better luck next time. Don't try to pin down a Loup Garou with gunfire that doesn't include silver bullets. Not going to work.
If the narrative of the block does interfere with the action being proposed, the counter action must overcome the action, and is under normal circumstances an action no matter what, "with benefits for extra shifts if the roll beats the block strength by a wide margin."
So the person chasing your Wizard would be prepared to spend an action to break the block. If they succeed by an extreme margin, then it might turn into a supplemental action, or they just might get benefits of the shifts for their next action. Depends on the situation. But a block is powerful for a reason when used effectively. It blocks and makes the other spend resources on getting through the block.
One thing to also keep in mind. Creating the block is the character's action for the exchange. So there is a tradeoff. In the same exchange that the wizard creates the block- he can't move. He's creating the block. The other then gets a chance to get through the block. The wizard can then take off running (with a sprint action). He doesn't get to run and set up the block at the same time. That sort of evens out the risks of taking this action.