Clark returned a fumble 65 yards for a touchdown, tying the Ravens' game at the Colts at 7 late in the first quarter.
This marked Baltimore's sixth defensive touchdown in its past 10 road games.
Ravens cornerback Marcus Peters ripped the ball away from Colts running back Jonathan Taylor, and Clark picked up the ball and sprinted down the sideline. After breaking free of a couple of tackles, Clark leapt over Indianapolis quarterback Philip Rivers at the Colts' 30-yard line before reaching the end zone.
It was a much-needed play for a depleted Baltimore defense, which is playing without All-Pro cornerback Marlon Humphrey (tested positive for COVID-19) and defensive end Calais Campbell, who left in the first quarter with a calf injury.
The Ravens have forced a turnover in 21 straight games, the longest active streak in the NFL.