Michael Lewis -- the man accused of stalking Caitlin Clark -- appeared in court on Tuesday and immediately made waves ... exclaiming he was "guilty as charged" before the proceedings even got started.

The bizarre scene all unfolded inside of an Indiana courtroom ... just two days after Lewis was arrested in Indianapolis on allegations he sent harassing and disturbing messages to Clark throughout December and January.

The 55-year-old Texas native -- wearing an orange jumpsuit and handcuffs -- was escorted into the courtroom by authorities ... and as he sat down -- he said out loud he was "guilty as charged."

The judge then informed him his statement was not necessary ... adding, "You have a right to remain silent, and I expect you to exercise that, OK? This is just telling you what the charges are."

Lewis, however, continued with his unusual behavior ... urging the judge to "throw me the booky." Several minutes later, he complained about his medication.

Eventually, Lewis was assigned a public defender ... and his official plea was entered as "not guilty."

As he left the courtroom, the judge again advised Lewis to "remain silent in the jail and only talk to your attorney."

Lewis -- who's facing a felony charge of stalking that carries a maximum sentence of up to six years behind bars -- signed docs ordering him to stay away from Clark ... and his bail was set at $50,000.

He's now expected to appear before a judge next in March.