TMZ Sports has obtained police video from the moment Glen Rice Jr. was arrested this week -- and cops were so shocked by the amount of cash he had on him, they suspect he robbed somebody.
We broke the story ... the ex-NBA player is accused of beating up another man in a grocery store parking lot and then running from the scene.
When cops tracked Rice down -- they searched his backpack and found $2,700 in cash ... along with 6 cell phones.
In the video, you can hear the cops talking about the money ... saying, "He has got a ton of cash. Tons of cash. I'm wondering if he robbed this dude. Mutual f***ing agreement that went bad."
Rice was initially booked for felony robbery, aggravated battery and marijuana possession -- but cops tell TMZ Sports officials are only moving forward with 2 charges ... aggravated battery and possession with intent to distribute.