An old timey version of rock'em sock'em boxing, with more awkward controls.
Use your mouse to guide your boxer (left guy) left and right. Hold the mouse button to "charge" (charge bar is located in the lower corner).
Higher charge does more damage but also uses more stamina (teal bar). Getting hit reduces stamina as well. Stamina is needed to do decent damage.
Stamina recharges over time.
The red bar is health.
Now get to it and knock that other guy out!!!