This isn't with my S2000 but with my daily 04 Civic ex coupe. I have it in manual (of course) and thought I'd go for a spin. I hit the nearest highway and roll start around 3000rpm on first gear redlining first than also second pushing both at WOT. After that when I tried to shift to third the gear locked as it was going in and it made a grinding sound. Stupid me instead of pulling it right out my instinct took over and I automatically tried to push it in (but failed). The whole "grinding" process was about 2sec. Will this harm the tranny? What kind of damage would I be looking at? I pushed the car none the less for about 5 miles after that driving in the same manner doesn't seem like the car was affected much cept I think the third gear has less pull now (maybe itz all in my mind).

Tuner

 

Your gear is fine from what you might have caused, but why it's grinding in the first place is what I would worry about before anything else.

 

Yea I was wondering about that too...every so often the third gear locks or struggles to be shifted fully. It "crunches" to fit and feels like the synch. can't keep up with the shift speed. This is all on normal driving around 20% throttle at 3000~3500rpm. Very weird....

Tuner