I've blogged this in the past, but quite simply, conditioning is vital. I am reminded of this daily. It's so much more than just energy systems. Specificity of movements (or non-specific a la "cross training"/variation), velocities, sensory stimuli, nutrition and hydration levels, sleep, and pyschological states.
I am not going to advocate the idea of old school aerobic base (actually I am, just different methods), but I will say a conditioning base. It comes down to being fit and it doesn't just start in the first few weeks (or last few) of the off-season or pre-season; it's year round. There are adaptations that have to take place throughout the body that needs time, just as building strength, speed and power do.
There's nothing magic or secret about it, just that very fit athletes tend to fare better than those that take many minutes to regain their breath (and composure) following a simple warm-up or agility drill... and a de-conditioned athlete, I would argue, is more likely to get hurt than one that is well-tuned.
Can you run/sprint well, change direction over and over, move your body in a multitude of ways with a quick tempo, all while being able to get the heart and breathing rate to fall quickly back into a comfortable zone upon completion?
Everybody lifts hard. Everyone does some plyos. Everyone sprints and does some agility work. Not everyone conditions (year round). It can be specific conditioning sessions or just sequencing and pacing of the movements, lifts, and/or drills one is already doing. Athletes can look very impressive in the weightroom or run fast or jump high on precise performance tests but once the real game starts, is the tank empty after the first few minutes. Speaking of the beginning of a competition, pre-contest anxiety can really compound this, making conditioning, again, very important from an ability to recover from this, but also the familiarity of having actually gasped real hard for air before and the confidence to know we are in shape for the entire duration.
But remember that there's balance that needs to be applied, because while conditioning is critical, it cannot destroy ones ability to develop more speed and power... but being more fit (in the correct domain) should enhance this. And, considering the current state of things, I am not too concerned that many are really conditioning too hard... outside of some endurance athletes. (That seems to be a common thread; endurance athletes need less conditioning, while other intermittent sprint sports need more... )
Survival of the fittest... and not just who falls off the wagon; get fit and stay fit so everyone stays on. It comes down to the most highly trained and physically energetic, and the symbiotic relationship between those two traits.
I've mentioned Walter Payton before; another that comes to mind is Jerry Rice... who was influenced by his then teammate Roger Craig. These guys made Montana's job easy. Ahhh the good old days...