Whenever a fielder makes a throw that stays straight as an arrow all the way to its target, it is commonly referred to as a frozen rope. If you see a throw like this, it looks very impressive right away as it is hard, fast, and straight, and is usually followed by a loud pop in the glove of the player catching the ball.
Frozen ropes are usually used in reference to outfield assists when a runner is gunned down. Vladimir Guerrero was notorious for making frozen rope throws from the right field. If a player had the guts to try to take an extra base when a ball was hit to Vlad, they usually paid dearly and typically were out before they even started their slide.
Throws from shortstop and third base can also be considered frozen ropes based on the distance of the throw. One of my favorites was definitely Rafael Furcal when he was playing for the Atlanta Braves. He had a cannon and would constantly fire frozen ropes across the diamond whether he needed to or not.
Catchers could garner this praise as well with a well-timed throw to get a runner out trying to steal a base. Pop times are always important for a catcher, but throwing under two seconds doesn’t mean anything if it has a slice like an amateur golf swing. A catcher’s throws have to be straight and on the money just like a frozen rope would suggest.
Arm strength usually isn’t given as much attention as a player’s offensive ability, but it is critical to make tough plays with runners always moving around the bases. Speed kills, but even Billy Hamilton would have a tough time scoring on a fly ball to right field with someone like Roberto Clemente waiting to catch it and make a throw to the plate.