R1 on first base, no outs. Ground ball to shortstop, who quickly gets the force out at second. R1, running a straight line from first, remains standing, and the relay throw from the second baseman hits R1 in the chest. Interference?


This is Runner Interference. Both the Runner from First and Batter-Runner are out.
RULE 8.4.2b
“Does not legally slide and causes illegal contact and/or illegally alters the actions of a fielder in the immediate act of making a play

The force-play slide rule is widely misunderstood at all levels. In all rule sets (NFHS, NCAA, pro), there is no requirement for players to slide. If a player slides, however, it must be a legal slide. On the double play at second base, the runner must either peel off away from the base to not interfere with the throw or slide legally. Another important point: Interference on this play is not contingent on if the batter-runner would have been out or safe at first base.