5/20 -- 8:02 AM PT -- Authorities have released Austin Maddox's mugshot ... and he appears a bit beaten up, with red marks on his face, and what looks like a partially swollen eye.

Former MLB third-round pick Austin Maddox was arrested during an anti-child predator sting in Florida last month ... and now, the ex-Red Sox pitcher is facing several felony charges.

The Jacksonville Sheriff's Office released the results of its five-day "Operation Valiant Knights" bust on Monday ... claiming 27 men believed they were communicating with underage girls online -- but in reality, they were speaking to detectives.

33-year-old Maddox -- who appeared in 13 career games -- was arrested on April 28 ... and charged with traveling to meet after using a computer to seduce/solicit/lure a child, solicitation of a child via computer to engage in sexual conduct, unlawful use of two-way communication device, and produce/promote performance which includes sexual performance by a child.

His bond was set at just over $300k.

Sheriff T.K. Waters addressed the arrest in Monday's press conference ... saying, "Austin Maddox, a former Red Sox MLB player, traveled with the intent of engaging in sexual activity with a 14-year-old child."

Law enforcement released video that it claims shows Maddox getting busted. You can see him exit a red pickup truck and walk into a home as he comes face-to-face with several officers.

Maddox was immediately tackled to the ground and placed in cuffs.

Maddox is due in court next week.

The former Florida Gator spent just one season in the big leagues before retiring a few years later.