The video shows a portion of the field sobriety test. Short is chatting with a couple of police officers, and then suddenly takes off (at about 25 seconds into the video). However, he trips on the sidewalk (gracefully) and is subdued quickly.
Not only was Short booked for DUI, police say they also found drugs in their -- not his -- vehicle, when they arrived at the station. For his part, Short said the following (as reported by his rep):
Short was diligently searched and cuffed prior to being placed in the disgustingly filthy patrol car.
It was 3 AM, the cop car smelled like vomit and was littered with remnants from prior arrests of the evening.
To make a long story short (no pun intended), Short was saying that the drugs -- reportedly meth or ecstasy which was possibly laced with meth -- were left in the car by the prior arrestee.
The rep also explained Short's attempted race to freedom:
In the past, Short, like many others, has been mistreated by law enforcement and these unfortunate prior incidents led to the complications after the stop.
In addition, the rep added that the idea of Short carrying any sort of powder was silly:
Any assertion that Short was carrying powder is ridiculous! Every rap fan knows Short's into weed.