Air carrier Captain reported the flying FO accidentally engaged the go-around switch during initial approach and an unstable approach ensued.

Narrative

While descending on the arrival into ZZZZ; (ZZZZZ); the FO was the PF and he inadvertently hit the GA (Go Around) switch (with the flap lever set at flaps 1) while passing thru 6;000' MSL in a 1;280 FPM descent (all the following altitudes and VVIs (Vertical Velocity Indicator) are taken from a website and I deem them appropriate). After the go-around was initiated; we began climbing at a rate of 2;112 FPM and accelerating (a total change of 3;392 FPM in the weather at night on the approach). The FO kicked off the autopilot and pushed the nose over such that at 5;750' MSL we were now descending at a rate of 2;432 FPM (an abrupt delta to go from climbing at 2;112 FPM to descending at 2;432 FPM; a delta of 4;544 FPM with a 280 ground speed thus overspending the slats since we were at flaps 1). My thoughts went immediately to a possible accident so I intervened and took control of the aircraft before the descent rate and airspeed put us in a very bad position. I was disoriented because this happened within seconds and we were night/IMC thus complicating the situation. My unusual attitude training immediately kicked in and as we were passing 4;500 MSL with a vertical descent of 2;816 FPM; I verified wings level and pulled to the horizon while extending the speed brakes to slow down. I felt like I had the aircraft under control by the time we were passing 3;100' MSL with airspeed below 250 KIAS.This event started at 6;000' and we recovered mostly stable by 3;000'. By this time though; we were off track and we were exceeding the max allowable airspeed at ZZZZZ1 (200 KIAS max) by almost 50 knots. Approach started asking us about our airspeed and directed us to slow down. I was still hand flying at this point trying to reconfigure and reestablish ourselves on the arrival and approach. For some unknown reason; I continued hand flying the approach to final and got probably 300' low at one point while trying to re-automate the aircraft (I ended up turning both flight directors off and then back on). Once I did that; we were able to select auto approach and slow down to configure normally. I just flew the entire approach and landing by hand. We landed uneventfully.I have absolutely no idea why or how the first officer engaged the Go Around lever. He says it was inadvertent so I have to believe him. But I will say that in my 29 year career flying for this company (20 as a Captain); I've never once had to take the aircraft from the first officer. I was completely calm and relaxed one second; and then pegging the startle index at 100 three seconds later. Thinking back about the situation; had I just selected altitude hold and put the autopilot back on; the aircraft would have stabilized quicker and we could have gotten vectors back around on a more stable approach. The approach and landing were uneventful after I intercepted the localizer and glide slope; but I was really frazzled and would have done better going around.Suggestions: Don't play with the go-around switch while on a descent to landing.