Coaches need to stay in shape too. Coaches have a lot going on. Many teach in addition to coach, so obviously an efficient workout is one that might actually get done. You should be able to be done with this workout in less than 20 minutes even if you loaf.
I say this is a workout for the coaches, but this will be effective for your athletes as well.
To be done on two different days per week. Ideally with at least two days rest between.
One set to failure. If you can't get at least 8 reps in a 3/3 cadence, decrease the weight. Or don't pay attention to reps at all. Just time your set and work to fail between 45 and 90 seconds. If you fail before 45 seconds, decrease the weight if it was before 30 seconds otherwise stay with the same weight. If you can go considerably past 90 seconds, increase the weight.
This will give you all the stimulus you need for strength and muscle gains. Worried this isn't enough? Then you aren't working at a high enough intensity. Failure means you can't do another rep in good form no matter how hard you try.