You sound like
Fore (or for).
A base for protest in December
Deforce - fore 'in' Dec - meaning to unlawfully withhold land or property from its true owner. If this occurred it would be grounds for protest. There is a documentary Deforce on the history of Detroit.
This is the best I can think of, other being Forefathers' Day though not a strong explanation for the base for protest.
The sweater for a special member
The sweater may be skin. Append this and use your imagination as to what the special member is.
A kiss or stroke, with sport or game
Foreplay - this is kiss/stroke. Play (sport/game) is added to fore.
Before your eyes, a prophet's claim
Foresight - a prophet's claim. Sight which is 'what is before your eyes' is added to fore.
The road that splits before nineteen
Fork - using For and adding K which is the chemical symbol for Potassium atomic number 19.
When stung, I am what once has been
Before - the prefix sounding like bee for a stinger.
A valued rock, when minus one
Ore - a rock source of metals after subtracting one letter.
I cross a stream, with aid from sun
Ford - a shallow river crossing.
For plus vitamin D which is manufactured in human skin cells with help from sunlight UVB rays.
A hint at future, free from light
Foreshadow - add shadow which is free from light.
The cry for sphere that's out of sight
Shouting fore when a golf ball is hit as a warning.