The keys to a good throw on a slow roller are quickness, efficiency and arm slot. When the softball is coming at you, you need to move forward to attack the ball. If the ball is too slow or stopped, you may need to field the ball barehanded in order to speed up the play. After fielding the softball, get rid of it quickly, using a lower arm slot than normal when throwing off your right foot. The release point is actually below side arm. When the ball is released, the ball will tail and sink. Since it is not a spot from which you’ll be accustomed to throwing from, you will need to get used to the ball flight and make sure that you start the throw in the right spot so that the tail and sink takes it back to the first baseman.
Practicing these throws will allow you to develop the feel and confidence to make this throw in a game. You should play catch from that arm slot about twice a week. You don’t have to do it a ton since it’s not the most natural thing, but after you’ve gotten your arms loose, try playing catch with a fellow infielder. The distance between you and your teammate should be a little shorter than where you would normally play catch. The more you practice this play, the more you will be prepared to make it during games.