Final answer:
Pointing a realistic-looking toy gun at another person constitutes assault because it creates a reasonable apprehension of imminent harm. The other scenarios lack either the intention or the reasonable apprehension of harm necessary to qualify as assault.
Step-by-step explanation:
Among the provided scenarios, action b. Pointing a realistic-looking toy gun at another person constitutes assault. Assault is an act that creates an apprehension in another of an imminent, harmful, or offensive contact. It involves an intentional act by the defendant and requires no actual contact or injury, but rather the reasonable apprehension of a harmful or offensive act. In the context of the question, pointing a realistic-looking toy gun at another person is likely to induce fear or apprehension that they may be harmed, thus satisfying the elements of assault.
The other scenarios listed do not meet the criteria for assault. A bystander being hit by a ball during a sports practice is typically accidental and lacks the intentional element required for assault. An 8-year-old threatening a 13-year-old with a water balloon likely would not create a reasonable apprehension of imminent harm due to the nature of the threat and the ages involved, and one student bumping into another in a crowded hallway is generally unintentional and caused by the circumstances rather than an intent to threaten or harm.