This is mostly nerdy reply about the actual attack you chose. Apply as desired.
There are several things catching my attention with this attack:
-it is using the spear one-handed
-it is starting from an idle/relaxed hold moving instantly into the thrust.
-there is a twisting motion, as well as a thrusting motion.
-he has a shield but he doesnt use it.
Lets examine this a bit further:
-using a spear onehanded has several disadvantages, especially in a thrusting attack. you cannot accurately thrust at a specific point, which is kinda the idea with a spear. your only method of adjusting the final location of the tip is the twist of the wrist. Due to the length of the spear and the resulting leverage it will result in very a inaccurate and also weak attack.
-the initial twisting/turning of the spear in 90degrees just amplifies the problems mentioned above. you will hit even less reliably, and the twisting motion will reduce the thrusting power. your attacking direction is forward but the spear tip's momentum is going downwards, and with the lack of control from using only one hand you'll end up with a really bad thrust.
now considering these points, one possible thrusting motion could be: his shield arm grabs the middle of the spear (right above the right hand's position) grips it tight and thrusts it forward while the right hand slides back controlling the direction of the spear.
This will also make him utilize his shield, so that he's blocking attacks from the front while preparing and executing the attack(i.e. grabbing his spear).
Weak explanation but i hope you get the idea.
The reasoning behind this is
-utilizing the whole length/range of the spear.
-strengthening the thrust by fixating it in the middle of the pole.
-controlling it at the far end for pinpoint attacks or quick motion adjustments