The coach noticed that Caleb really started to kick the soccer ball with great amount of power after the kicking drills. Caleb adjusted the power of his soccer kick by

increasing the speed of his kicking leg prior to and upon contact with the ball
starting his kick from a two legged standing position prior to contact with the ball
stopping his motion upon contact to create more of a rebound effect <-(I think its this one)
turning his foot and using the inside of his foot and ankle to strike the ball

The correct answer is:

Caleb adjusted the power of his soccer kick by stopping his motion upon contact to create more of a rebound effect.

It seems that the correct answer to the question is "stopping his motion upon contact to create more of a rebound effect." This means that Caleb adjusted the power of his soccer kick by stopping his motion upon contact with the ball, which allows the ball to rebound off his foot with more force.

To arrive at this answer, I analyzed the given options and considered their relevance to increasing the power of a soccer kick. Let's go through each of the options:

1. Increasing the speed of his kicking leg: While increasing the speed of the kicking leg can contribute to more power, it alone may not be the most effective method. It is important to note that the question specifically mentions Caleb adjusting the power after the kicking drills.

2. Starting his kick from a two-legged standing position: While this technique may provide stability and balance, it doesn't directly address increasing power.

3. Stopping his motion upon contact to create more of a rebound effect: This option aligns with the question's context. By stopping his motion upon contact with the ball, Caleb can transfer more energy to the ball, resulting in a more powerful kick.

4. Turning his foot and using the inside of his foot and ankle: This option refers to technique rather than specifically increasing power. While using the inside of the foot and ankle may improve accuracy and control, it may not directly address increasing power.

Therefore, based on the options provided, the most suitable answer is "stopping his motion upon contact to create more of a rebound effect."