This is an excerpt from Teaching Fundamental Motor Skills 4th Edition With HKPropel Access by A. Vonnie Colvin,Nancy J. Egner Markos & Pamela J. Walker.
While many people believe the only purpose of underhand throwing is pitching a horseshoe or playing cornhole, it is in fact an integral part of many sport skills. Underhand throwing is essential to softball pitching, and underhand tossing can be used to assist a fielder in making an out from a close distance in softball or baseball. In addition, the critical elements of underhand throwing are very similar to those of the underhand volleyball serve. With the addition of a racket, underhand throwing is essential to the game of badminton.
Often, the purpose of underhand throwing will dictate exactly how it is performed. Activities requiring height (e.g., slow-pitch softball pitching and horseshoes) will require that the follow-through be exaggerated. When the distance to the target is short or if the objective is speed, then the follow-through will be much shorter (e.g., in fast-pitch softball pitching). In this section, we emphasize the skills most relevant to young children—that is, those throws requiring an arc.
One factor that greatly affects the initial learning of the underhand throw is the target placement. If a target is placed at a low level, the student might roll rather than throw the ball. If the target is at a high level, the student is more likely to develop incorrect throwing habits. While students are learning and practicing this skill, a medium-level target is best. Once the students understand how to perform the skill, then we encourage the use of large targets placed at a variety of heights.
National Standards and Grade-Level Outcomes for K-12 Physical Education (SHAPE America, 2014) (table 4.1) indicates that kindergartners should be able to throw underhand with the opposite foot forward (S1.E13.K). First graders should be able to throw underhand demonstrating two of the five critical elements (S1.E13.1), and second graders should be able to use a mature pattern (S1.E13.2). In grade 3, students should be able to throw underhand to a partner or target with reasonable accuracy (S1.E13.3). Students will begin using the skill more in grades 4 and 5.