The rapper was the special guest Saturday for "College GameDay" -- where analysts and pundits sit around talking shop about all the games going down for the day ... and who they got to win, etc. Jack was on the panel too ... but first, let's start with his performance.

JH was at Ohio State here -- who are playing Notre Dame today -- and as he was introduced on a tiny little stage while surrounded by students ... things fell flat fast.

He was doing his song, "First Class," for the kids ... but it became pretty clear that they just weren't into it. Take a look at the reaction from the crowd -- yes, some toward the front are a little hyped ... but most everyone else is just looking on, like deer staring into headlights.

Jack seemed to notice the lack of energy too -- at one point, he appeared to throw his hands up, as if to say ... WHAT THE HELL, GUYS?!? It was very Ja-Rule-At-The-Bucks-Game.

Still, ever the professional ... Jack powered through, and word is he did damn near the whole song -- which is also getting mocked right now. Namely, the fact that nobody at ESPN thought to just pull the plug and move on. The jokes are flying in every direction over this.

That wasn't the only thing that left an impression, though ... Jack's actual football IQ was on display during his sit-down portion of the broadcast, and there too he's leaving 'CGD' viewers less than impressed ... but certainly entertained.