A 22-year-old Fitchburg man is facing charges after Janesville police say he was caught in the city with a handgun.  Police say officers responded to a physical disturbance in the 2300 block of Harvard Drive about 7:00 p.m. Sunday.  Officers say Marquis Maier tried to flee into an apartment, but was taken into custody with the use of a taser.  During a search of Maier, officers say a loaded firearm was found in his pocket.  Police say Maier is currently on felony probation in Dane County for Burglary and Aiding a Felon.  Officials say Maier is being held at the Rock County Jail on charges including Felon in Possession of a Firearm and a Probation Warrant.