I've been shooting high school bands for near a decade now. Your question as asked is hard to answer because there are too many variables you have left out.

• What type of photos are you after? Wide angle shots with a large portion of the band or closeups of individual members?
• What will your shooting position be? In the stands (how big is the stadium and how far are the stands from the sideline)? From the sideline? From on the field at times?
• How many students are in the band? How are their shows written? Do all of the members circulate and spend some time on the front line at some point during the show or do certain sections tend to be placed at the back for most of the show?

Without answers to these types of questions it is hard to give a good answer on what type of lens(es) you will need. However I will share what has worked for me at various stages in my experience.

I started out with a Canon Rebel XTi and two lenses: the EF-S 18-55mm kit lens and an EF-S 55-250. The current 18-55s are much better than the one that came with my XTi (which was horrible), and I replaced it with a Tamron 17-50mm f/2.8 Di II that I used as my "wide" lens until I went Full Frame a few years later. For the wide shots I highly recommend this lens. I got some pretty good stuff with the XTi, the 17-50 and the 55-250.

Rebel Xti and 55-250 @ 154mm, f/5.6, ISO 800, 1/100 second

Rebel XTi and 17-50 @ 39mm, f/4.5, ISO 800, 1/100 second

Being (self) limited to ISO 800 forced me to use slower shutter speeds than I would have liked. I had to take a lot of pictures and work on timing them perfectly to get a few that were timed so that the motion blur was minimized.

By the third season I had picked up a Canon 50D and an EF 70-200mm f/2.8 L IS II. It was like walking out of the darkness and into the light! The camera handled much faster allowing me to catch more shots I would have previously missed and the fast, high quality telephoto allowed me to shoot at faster shutter speeds.

If you are going to limit yourself to only one lens, a 70-200mm f/2.8 is probably the one you want. You can shoot (from the sideline) closeups of students near your shooting position, full body shots of students out to about the nearest hash mark, and also (from the stands) wider shots of groups of students such as a particular section. Get the best one you can afford. IS is nice, but not essential, especially if you practice good camera stabilization techniques and/or shoot from a monopod. If the choice is between a 70-200 f/4 IS and a 70-200 f/2.8 (no IS), go with the faster aperture! I've gotten a lot of nice shots with the 50D (and later the 7D and 5DIII) plus the EF 70-200mm f/2.8 L IS II!

This one was from the very first time I shot with the new lens. Canon 50D and EF 70-200mm f/2.8 @ 120mm, ISO 800, f/2.8, 1/200 second. It has been slightly cropped. In the full resolution version you can see the weave of the mesh on her shoulder!

The faster telephoto lens allowed me to shoot at faster shutter speeds that enabled me to get shots I couldn't before and along with the better AF system of the 50D and the better optical performance of that amazing lens I was able to capture many more "keepers" than before. I continued to use the XTi and Tamron 17-50mm f/2.8 for my wide shots. With wide shots the shutter speeds are less critical, since the same movement at the same distance produces less blur. Using two bodies allows me to change from long to wide and back almost instantly.

I currently shoot with a recently acquired 7DII + the 70-200 (still a great lens). The AF system of the 7DII is much more consistent than my 7D (it replaced the 50D after about 3 years of heavy use). I'm looking forward to seeing how well the "anti-flicker" feature of the 7DII works with typical high school stadium lighting.

(Update: The new anti-flicker feature Canon introduced with the 7D Mark II is very nice and almost revolutionary for this use case. Not only does it give much more uniform brightness and color in each frame when shooting under flickering stadium lights which has dramatically increased my "keeper ratio", but since it always releases the shutter at the peak of the lights' cycle I can shoot about 2/3 stop faster than I could under the same lights with the same ISO and Av as before! Note that when shooting wide enough that light from more than one tower is in the scene if the towers are out of phase with each other then it doesn't work as well, but it still does better than without the anti-flicker feature.)

I now use a 5DIII for my wide body (the first season I had it I alternated it and the 7D with the 70-200) and depending on what I am going for usually use either an EF 17-40mm f/4 L or a 24-105mm f/4 L IS. Sometimes I'll also add a 5DII and a 50mm f/1.4 or 100mm f/2 into the mix, but I prefer two bodies unless I have a specific shot in mind that only the fast primes can get me.

EOS 5DIII and EF 17-40mm f/4 @ 17mm, f/4, ISO 1250, 1/200 second.
Okay, I cheated! This shot was from the practice tower during a full dress run before a game during mid-October. The sky was overcast and sunset was just a few precious minutes away.

Here's a shot from the stands at a competition in the late afternoon with an overcast sky. Canon 5DII and EF 24-105 @ 35mm, f/8, ISO 160, 1/500 second and a lot of post processing including tone mapping a single raw file.

The full frame bodies along with my increased experience dealing with noise in post processing has really allowed me to push the ISO in recent years. I'm no longer afraid to routinely shoot at ISO 2500 and even ISO 5000 with the FF bodies when the situation dictates it. I'll go as high as ISO 3200 with the APS-C bodies (avoid the +1/3 stop ISO settings on recent Canons: 125, 250, 500, 1000, etc). This allows faster shutter speeds and, along with the better AF performance of my current gear, greatly increases my "keeper rate" from the days when I was starting out.

Beyond the gear, here are a few tips based on my experience:

• Shoot as many closeups as you can during the early season when there is still some daylight at the beginning of the game. If your band does an on-the-field pregame, you can get a lot of good shots when they are playing while standing at attention and not moving during the national anthem. The extra light will allow you to reduce the ISO setting and still get faster shutter speeds (1/250-1/500 second or faster).

• Don't wait until the show starts. When the students are on the field and lined up ready to begin, they are standing still and you can get some lower shutter speed shots.

• Don't just shoot the show! Get shots of them from the time they arrive to the time they go home. Lining up to march into the stadium, playing songs in the stands, warming up for halftime, marching out of the stadium, at practice, etc.

• Change your shooting position from one performance to the next. If you can catch a practice or two, work out a shot list for each shooting position. Actually take shots from the possible shooting position while at the practice and then revue them before you shoot the show from that spot to see which angles work for which parts of the show.

• Learn the show! The more you know what is going to happen next, the better you can plan ahead and get better shots. It allows you to be proactive in your approach rather than reactive. Develop a list of shots you want to capture at each performance, but also look for interesting things that you haven't noticed before.

• Develop a good working relationship with the band director. The more the director trusts you, the more access you will have to everything going on. I have even shot parts of shows from in the middle of the band on the field! In those cases I always attend a rehearsal and plan and rehearse my movements along with the band. Not only does this allow you to know where you can and can't move at a particular spot in the show, but it allows the students to be confident that you won't get in their way. It helps to do this later in the season when both you and the students already know the show fairly well. Even if you don't get in the middle of the band, you can still shoot from the edges on the left and right if you know exactly how far they will come towards you before they turn and go a different direction, or shoot from a low position behind the pit!

• To effectively use a wider angle lens, such as the EF 24-105mm f/4 L IS, for anything other than large group shots, you're going to need to shoot from positions very close to the performers. If you won't have that kind of access, then a wide angle lens should not be your only or primary lens, but can be quite effective as a second lens.

• To show just a bit of motion with the guard and percussion section use a shutter speed of around 1/160 to 1/250 second. You can freeze the face and torso while seeing a little motion in the hands and flags, sabres, rifles, drumsticks, mallets, etc.

Canon 5DII and 17-40mm @ 17mm, f/4, ISO 2500, 1/250 second from a kneeling position behind the pit (on the sideline out of view from the folks in the stands).

Canon 5DIII and 70-200 f/2.8 @ 200mm, f/2.8, ISO 1250, 1/160 second from a standing position on the 30 yard line at about the first hash mark (outside the band's formation, but on the field)

Canon 5DII and 24-105 f/4 @24mm, f/4, ISO 3200, 1/200 second from about the goal line and halfway between the sideline and the near hash mark. The stadium we were visiting only has four light towers centered over the 10 yard lines so the middle of the field is about 1-2 stops darker than the ends of the field. The band had a show that included a guard segment down near one of the end zones, so I planned and shot the show from that angle in that stadium and used the unique lighting to my advantage.