Dallas Mavericks Star DeShawn Stevenson -- Rookie Tattoo Artist

Dallas Mavericks star DeShawn Stevenson has a fallback plan in case the new NBA deal falls apart -- TATTOO ARTIST -- and TMZ has learned he got his first crack at human flesh earlier this week.

The honchos at Fallen Sparrow Tattoo Co. tell us ... Stevenson rolled in with friends Monday ... but instead of being the canvas, the NBA star thought it would be a good idea to take the needle and do some designing on someone else.

We're told DeShawn's favorite tat artist, Chad, volunteered for the mark -- so Stevenson grabbed the needle and inked the guy's leg with his jersey number, 92.

Fortunately, only the usual amount of blood was shed ... and Chad tells us, "For a first-timer, he actually did a pretty good job."