Focusing intensely, Elijah dribbles the basketball across the court.
The modifier in the sentence is "focusing intensely". The modifier should be as close as possible to the word it modifies. In the first sentence, the modifier "focusing intensely" is closer to "basketball" than Elijah. In the second option the focus and intensely is closer to "court". However, these things are not what is focusing intensely. In the third option, the comma actually separates two complete ideas and separating Elijah from the modifier. The last option is the best one because the modifier is an introductory appositive phrase and it is just before the word it modifies.