Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 141.47; Flight Crew Total 26000; Flight Crew Type 9699.97
Communication Breakdown; Fatigue; Training / Qualification; Troubleshooting; Workload
Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Human Factors
We were descending on the ZZZZZ1 STAR. Just prior to level off at a higher altitude; the controller cleared us to descend via the STAR to 12;000 feet. The PF pointed to the altitude as I set it. However; he went out of VNAV to FLCH because he thought he heard descend to 12;000 feet now. I was busy with a frequency change and getting the new ATIS; and I missed the change in pitch mode. When I looked up; I noticed we were approaching 15;000 feet even though the fix just ahead of us had a at or above 16;000 foot restriction. I called it out and the PF immediately leveled off at 15;000 feet. I immediately informed the Controller and asked if he wanted us to climb back to 16;000 feet. He said we could just 'descend to 12;000 feet.'  There was no conflict with other traffic.I believe this occurred for a number of reasons. It was a very difficult 3-day pairing made longer because of COVID. We were all exhausted; it was a high-workload environment; and the PF had not flown in over a year. He had trouble hearing ATC the entire trip which we attributed to his being off a year. Obviously; there was a breakdown in Verbalize; Verify and Monitor. Lesson learned: especially when tired and in a high-workload environment; strict adherence to SOP is essential.
Air carrier Captain reported the PF overshot the assigned altitude during arrival and attributed it to fatigue; workload and the PF had not flown in a year.