The following rule update was posted by NCAA on April 2, 2018:
If an obstructed runner crashes into a defensive player holding the ball, the crash takes precedence over the obstruction. The runner cannot simply run into the defensive player and not make an attempt to slide or go around the player. The runner must follow the guidelines in Rule 12.13 Collisions.
Rule 12.13.2 To prevent a deliberate crash ruling, the runner can slide, jump over the top of the defender holding the ball, go around the defender or return to the previous base touched. Excerpt from Rule 12.13 EFFECT: The ball is dead…If an obstructed runner deliberately crashes into a fielder holding the ball, the obstruction call will be ignored, and the runner will be called out. If the act is determined to be flagrant, the offender will be ejected without warning. (Behavioral ejection; see Rule 13.2.1.)
In addition, since a crash ruling is considered a form of interference, other runners must return to the base
they occupied at the time of the crash (interference).
Rule 188.8.131.52 A runner may not remain on her feet and deliberately, with great force, crash into a defensive player who is holding the ball and waiting to apply a tag. Ruling: If a runner is obstructed by a fielder without the ball (e.g. when the fielder is blocking the whole base/plate or base path) but the runner collides flagrantly with that fielder, the runner is ruled safe on the obstruction but she is ejected.
Excerpt from Rule 9.5.3 EFFECT: …If the runner collides flagrantly, the ball is dead, and although the runner is declared safe on the obstruction call, she is ejected. (Behavioral ejection; see Rule 13.2.1.). If you judge that this contact is incidental or unavoidable, the runner is ruled safe on the obstruction and she is not ejected. If an obstructed runner subsequently interferes with a defensive player’s reasonable opportunity to make a
play, interference is ruled.
Rule 9.5.7 An obstructed runner may not be called out between the two bases where she was obstructed unless one of the following occurs:
Rule 184.108.40.206 The obstructed runner commits an act of interference.
Rule 9.5.11 Should an act of interference occur after any obstruction, enforcement of the interference effect takes precedence provided both violations involve the same runner. For example, a runner is obstructed by the first baseman on a batted ball, but the batted ball strikes the runner in front of the second baseman who has a reasonable opportunity to make a play, or a runner is obstructed during a rundown but she deliberately interferes with a thrown ball.
Do not confuse this rule with the incidental or unavoidable contact on obstruction as noted above. If a defensive player is blocking the whole base/plate or base path without the ball, but incidental contact occurs while she is attempting to catch a thrown ball, this would still be obstruction, not interference.