91 NA rx7 240000 miles

I was driving out of a drive way. at 1st gear I rev it to about 6000rpm then shift. Heard a pop sound then I cant get the car in gear anymore.

If I roll the car down a incline I can push it in 1 st gear then it will drive. and I can shift it to second and third matching rpm.

I step on the clutch pedal and I feel the pressure plate vibration which is normal but it will not let the tranny disengage so I can get it in gear. What do you think broke?

Help Thanks.