For a foot entrapment, a weighted line (snag line) is dropped just downstream of the victim and worked back up stream. This can help dislodge the trapped foot and doesn't put rescuers in jeopardy of getting their feet trapped. You will be fighting the current and the force of the water on the trapped paddler. To really be effective, you need to snag the leg right about ankle height. This is why weighting the line to cause it to sink is helful.
An alternative and faster method is the sawing approach. Send a line across at water level just below the victim. Wade into deeper water on both ends. Now, move the snag line lower in the water by sawing back and forth while pressing down. If deep enough, you should be able to saw well below the knees and move upstream to dislodge the foot and free the victim.