Basketball Training Camp- Agility
You earn a star at 7,064 points.
So, if you get to around 7,060, you can skip ahead to drill 22, get 5 fitness points, rewind to the break before drill 22, sit through the 7 second break, and then get 5 fitness points on drill 22 again, rinse and repeat. You could theoretically earn a star about every 10-12 seconds if you're efficient. This results in about 5 stars per minute, or 17 hours to finish the achievement from scratch.
Let me know if you have any questions.
EricGarcia4 has a great solution. Unfortunately I noticed it does not work now since the workout is not available. I've been using the JJ Watt Football Training Camp - Stamina workout and replicating what EricGarcia4's solution states. (For note, this workout has a break in between each drill.)
I found out that you get one star between 4,438-4,445 (not sure which number is the exact star). If you can get to 4,430, do a workout to get AT LEAST 4,445, rewind to the prior break as soon as you have gotten to 4,445, rinse and repeat and you'll get a star each time you get to the threshold. The trick is to rewind not to the beginning of the drill you are on, but the break before the drill you are on to get the star. So, if the break is 20 seconds long, you could get a star every 25-30 seconds roughly. That's 120 stars per hour resulting in 42 hours to complete from scratch.
I'll be experimenting with other workouts to see if there is one that results in a quicker average stars.