The video doesn't offer much context, but from what we gather the puck had been shot in and bounced high off the glass. Rittich attempted to catch it but evidently forgot that there was a net in his way, leading to this sensational clip:
That's one that I'm sure Dave will want to forget as soon as possible. With Saros sidelined, Rittich will be Nashville's go-to in the postseason, and I'm sure the opposition will take any excuse to remind Rittich where the net is.