TMZ Sports has obtained the police report from the arrest.
"Seemed like a good place"TMZ Sports has obtained the police report from McGuire's arrest ... and cops say a witness told them the Blue Jays catcher had been masturbating in his parked car before they arrived on the scene.
According to the report ... cops say after they rolled up to the parking lot, they saw McGuire with his shirt "barely covering his genitals" and his sweatpants around his ankles.
They claim in the report when they got McGuire out of his car, he "had an erection which was very apparent."
Cops say McGuire apologized to them profusely for the incident ... saying, "I'm sorry, I'm so sorry, this is really embarrassing." Cops say McGuire added, "I really shouldn't have been doing that."
In the report, cops claim when they got McGuire's phone to try to find his current address ... they noticed an "extremely pornographic video was playing on the screen."
Officers say they asked Reese why he came to the parking lot instead of just going home ... McGuire responded that he "did not know, it just seemed like a good place."