Lots of people, young athletes in particular, put in a lot of work but don't necessarily get the results they want. The issue is that while sweat is required to get the gains you want, if you invest that sweat in the wrong exercises or programs you won't get the desired results. If a 100 meter sprinter wants to get faster, and spends his days running marathons, he is indeed working hard but his sprint times will probably get worse. This is the same premise for most team sport athletes - sweat doesn't always equal improvement.
I saw a video a friend of mine posted on facebook yesterday - it featured a few high school football players on a field doing a variety of different exercises in what he termed their "phase I" of the off-season. They were mixing in sets of flipping tires, jumping hurdles, running around cones, doing jumping jacks, sprinting, and a few other exercises, a crossfit style workout. I had two immediate thoughts - 1) it's great that these kids are willing to get to work and pursue their goals, and 2) it's a shame that their sweat could have been better invested.
Let's take a look at what they're getting out of that workout. They are most likely getting in better shape, improving heart health, and improving their conditioning. Also, they're bonding as a team and building trust between teammates, which can serve them well during the season. On the other hand, they probably aren't making big strength gains, or as good of strength gains as they could being on a more well structured program with basic tenants of progressive overload and strengthing specific movement patterns.
If we revisit the exercises shown in the video, we should note that nothing is wrong with any of the exercises. The question is, are they the right exercises for their particular goals? Are these exercises going to increase the players' maximal output and low rep max outs? Because for football players, that is largely what matters - how much force can you create in short bursts. Their workout doesn't match their goals, however, that workout might match someone else's goals. Each sport has different needs, and workouts can be catered to match. Generally, a good strength training foundation and progressive overload on the right exercises is the right path.
Working hard is a pre-requisite for getting reaching lofty goals, but it isn't the only pre-requisite. Working hard needs to be combined with working smart and directing your energy in the right direction. Don't just look for ways to make yourself sweat, look for ways to improve performance. Don't waste your sweat on the wrong exercises, and if you find a strength coach who's only looking for you to sweat and be tired, then keep looking. You need a strength coach who knows how to invest that energy to get the best returns.