Lots of ACCEPTED penalties on the defense can result in a loss of yardage for the offense but that generally is accompanied by the preservation of a down
Yes.
3/10, 50, 4:30 (4), A=10, B=12.
A12 advances to the B-44, where he is tackled and 'downed.' B55 was offside at the snap. Team A elects to accept the 5-yard penalty from the previous spot, which will place the ball at the B-45, and repeat 3rd down.
In most cases, Team A will gladly give up a yard to re-gain a down, especially late in a game, and they are behind in score.
But, I'm guessing this ain't the scenario to which Covid is referring.