Handwaving: Assume they can survive any force they apply to themselves
A 9 foot tall humanoid capable of sprinting at around 65 mph weighing about 600 pounds, what affect would he have if he ran on differing terrains? (well on the terrain itself) Would the terrain inhibit him? How?
BONUS:What kind of effect if he charged a human or a medieval building of some kind.
ALSO: I know the speed is super fast but it exists for story reasons and how they are that fast isn't relevant
There would be two somewhat different issues - one with acceleration, and one with running at speed.
Let's start with running. 65 mph is a very high speed for a bipedal creature. Your giant would have to push the ground much stronger than a normal sprinter just to compensate for air's resistance. Next problem is due to giant's big weight. The weight is 3-4 times more than normal. At the same time, feet surface is only 2-2.5 times large than normal (square-cube law, sorry). So, I would expect that during normal running the amount of ground pressure would be 1.5-3 times higher compared to a regular sized human.
That should be not an issue when running on hard surfaces like stone, but moving to dirt, grass, sand and mud should present a problem for your giant. Slowing effects of the soft surfaces would be disproportionally higher for a giant.
But the real problem would be acceleration. Cruising at speed has little requirements for the traction, but changing the speed (accelerating, slowing down and turning) puts athlete's shoes to a real test. If you played or watched games like football on a grass field, you might have noticed how the dirt is flying from players' feet at critical moments. It is becoming important to wear spiked shoes like cleats, because friction alone is not sufficient for adequate traction. You just can't play the same game when wearing sneakers, even good ones.
These traction problems would multiply for a giant runner. He would be having a very difficult time starting, stopping or maneuvering. Running on dry stone for him would be like running on wet stone for a normal person, and wet stone for him would feel like ice. Spiked shoes will become a necessity if he needs to run on dirt or grass. Interestingly, worst terrains like mud would actually provide better traction, so while the giant would be sliding in a thick mud, he would be sliding almost like a normal person.
Yes, terrain would inhibit him, it inhibits anything. Running through marshes is harder than running on a running track. His weight, $\approx 272 \text{kg}$ is pretty substantial, about four times that of an average person. So he will sink into ground a little easier - softer ground will be an even bigger problem since the force he needs to put in is more.
$65\text{mph} \approx 29\text{ms}^{-1}$
$E=0.5 m v^{2} = 0.5 * 272 * (29)^{2} = 114,376 J$
Now, hitting something with a hundred thousand joules of energy is going to cause it some considerable damage. Human, wall or otherwise.
To put this into perspective perhaps, this guy is comparable weight to a motorbike plus a normal person riding it so the effect will be something like a motorbike going 65mph into w/e you imagine. If it hits a person, the person has serious injuries if not dead. However going into buildings would heavily depend on how fortified the walls are but if the giant is well protected against self damage, it could do considerable damage to wooden walls.
