Magically knock someone down and pin them using Science
This question is going to take some set-up to understand the world it is operating in. This is a modern-day magic world that I've been building up. Magic exists, is hidden, and is quite powerful.
Concepts
Physics still works normally...magic just has the ability to supplant the normal rules for a while. Living things possess some level of spell resistance, increased as they are more magically powerful...so altering the body of a living target is much harder than altering their environment. It is much easier to generate a magical effect close to the body, than to do so remotely (at least for the style of magic I'm talking about for this question)
Magical Limits: Everyone who can wield magic is constrained by two limits on their power. Burst Limit and Sum Limit. Burst Limit is the amount of magical energy that you can channel in a moment, determines how 'big' a spell is. Sum Limit is the total amount of magical energy you can channel prior to exhaustion. Exceeding these limits can cause Bad Things™ to happen to you. A spell can be sustained and added to once it has been cast, but this isn't used by most magic users.
Function of spells: Magic is controlled entirely in the mind. However, controlling magic is hard and so most magic users will use words, gestures, prayer slips, etc as a form of classical conditioning to make it easier. 227
For example, if every time you sling a fireball, you say "Eldur" (Icelandic for Fire), then eventually you will condition yourself to mentally control magic into a fireball when you say "Eldur." Crafting a spell on the fly is possible, but requires a lot of concentration.
The Character
<PERSON> is a well trained Magus, but his burst limit is simply pathetic. His sum limit, however, is enormous. So, to simplify that a bit...he can produce magical energy at a slow, steady, nearly endless trickle. While this is pretty good for Enchanting or sustaining magics, it's pretty terrible at straight combat. His low burst limit means that if he tried to just fling a fireball on the spur of the moment, he might be able to make your hair curl a bit with a burst of heat. <PERSON> is also currently a student at a normal university, studying the sciences, looking for ways to work around his magical issues.
An Example of a combat spell, as produced by <PERSON>
<PERSON> uses his magic to begin gathering a static charge in the air around himself, keeping himself insulated from it. Once he has gathered enough electricity, he sends as much of an electrical shock towards his target as he can, and releases his hold on the gathered electricity. The rest of the electrical charge follows the path of ionized air created by the small jolt, resulting in what is effectively a lightning strike. This process takes about 60 seconds for a moderately powerful jolt (think stun gun)
The Question
<PERSON> needs a way to abruptly knock an opponent to the ground and keep them there without touching them. He is not aiming to kill, and is at fairly close range (so no creating a small bit of antimatter or anything). Using his understanding of the sciences, and the slow trickle of his magic, is there a way he can pull this off? It's okay if he needs some prep time before the spell goes off, as long as you can't tell he's prepping it by looking at him or being in the same room as him.
The situation in which he would throwing this spell down would be an urban environment, somewhere indoors. 300