charlienow Loc: Hershey, PA

Since you will only be taking pictures of the games for another year you might want to consider something with more range such as an 18-300 zoom or at least an 18-200. I love my 18-300 and use it almost exclusively with good results. It’s good for travel, lacrosse, soccer and other sports. I’ve also used it for graduations, weddings and other family gatherings. There is no limit to its uses.

Chuck

CWGordon

First: Although I generally stick with proprietary lenses, Sigma builds very fine lenses. They are not cheapos by any means.
Secondly: It can be very difficult to shoot long lenses without lots of practice. Shoot, shoot and shoot some more. It really is the only way to improve.
Third: I have shot lots of indoor sports. Way back when, for newspapers. Later, my nephews kids. 200 mm is a big jump, maybe 85-100 would be lenses more easily used. It might be that the larger telephoto is “cropping” too much and not giving the perspective that really highlights the action. The shorter lenses may give you more of what you want w/o the blur you may get with trying to hold a bigger lens in a more stable way.
Last: Don’t listen to everyone’s varying opinions. After a while you will find your pictures will get worse. Look for a few ideas that seem best to you and may be more easily adapted into what you are trying to do. It takes time to get good, at anything. Top professionals take thousands and thousands of pictures. Obviously they will get some great shots. However, they have plenty of failures, as well, just like everyone else. Enjoy what you do, you will get better the more you shoot.
Good luck and have fun.

wetreed

Tamron G2 Series lens are as good or better than OME lenses. I speak from experience.

jeep_daddy Loc: Prescott AZ

Ditto!

keywest305 Loc: Baltimore Md.

Canon and Nikon make a great lens but today the Tamron and Stigma have stepped up the game. I bought the Tamron 15-30 G2 24-70 G2 70-200 G2 45 1.8 and the 35 1.4 and they all are equal im my opinion to the latest Canon and Nikon. I have had all the lenses over the years from Nikon and love these new Tamrons

CWGordon

I still believe most proprietary lenses are slightly to a bit better. Still, I have a few lenses from Tamron and Sigma and am very satisfied. There are a few lenses these other manufacturers make that are slightly better than nikon or canon make. Prices have tightened on most offerings, as well.
Most users cannot tell a difference in the final results/images.

CWGordon

Tamron is way better than nikon and canon and sigma on warranty work. Sony is excellent. All of this should be weighed when selecting lenses for purchase. There is a cost to be weighed for value of “guarantees.”

MidnightManiac

I shoot a lot of sports both inside and outside. I'm not a pro but I find indoors using my Tamron 70-200 f2.8 to give the best results. Outdoor sports the Canon 70-200 L f4. At times use an extender for outdoor baseball. By far the best walk around lens is my Sigma 24-70 f2.8 art lens, great quality lens (not cheap). Love all 3 of these lenses for different situations. Sports I shoot with a 7D mark II, best sports camera I have ever owned. Walk around like my 5DII with the 24-70. If I had one lens for all it would be the "TANK" the Tamron 70-200 f2.8.

amfoto1 Loc: San Jose, Calif. USA

The most direct upgrade from your 18-55mm is the more premium Canon EF-S 17-55mm f/2.8 IS USM. It's one to two stops "faster" than your 18-55mm (depending on focal length you've selected with the zoom). It's also better built, faster focusing and has better image quality. Of course, it's more expensive, too.

If you want a longer focal length, the most logical would be an 24-70mm f/2.8 or an even longer 70-200mm f/2.8. That's about the upper limit of focal length you will need on an APS-C camera inside a gym. These both get you up to two stops more light, as well as more "reach" than you have now. The Canon EF versions of these are all premium L-series, which means they will be excellent, but quite expensive. The Sigma are a somewhat more reasonably priced alternative, with good overall performance though not quite as good image quality as the premium Canon lenses. All these 24-70/2.8 and 70-200/2.8 are full frame compatible lenses, which means they will be relatively large and heavy (your 18-55mm and the EF-S 17-55mm are both "crop only" lenses, which allows them to be smaller and lighter).

Comparisons (info from B&H Photo):

EF-S 18-55mm f/4-5.6 IS STM ($250), approx. 2.5" x 2.5", 215 grams (7.6 oz.)
EF-S 17-55mm f/2.8 IS USM ($879), approx. 3.25" x 4.25", 645 grams (22.7 oz.)

Note: The EF-S 17-55mm lens is not an L-series, so doesn't include the lens hood. That's sold separately for $50. OTOH, this lens has been around for a while and is widely available at lower prices on the used market.

EF 24-70mm f/2.8L IS USM II ($1899), approx. 3.5" x 4.5", 805 grams (28.4 oz.)
EF 70-200mm f/2.8L IS USM III ($2099), approx. 3.5" x 8", 1480 grams (52.2 oz.)

In general, Sigma lenses tend to be "over built" and among the heaviest.

Sigma 24-70mm f/2.8 DG OS HSM ($1099), ~ 3.5" x 4.25", 1020 grams (36 oz.)
Sigma 70-200mm f/2.8 DG OS USM ($1379), ~ 3.75" x 8", 1800 grams (63.5 oz.)

I use several lenses around the size and weight of the Canon 70-200mm f/2.8 above, usually hand held and for long periods of time (shooting sporting events). The cameras I use them upon are bigger and heavier than a T81 (a pair of 7DII and a 5DII). Plus I have battery grips on my DSLRs, further increasing their weight and mass. I feel it makes the balance better with larger lenses (among other advantages). There isn't a battery grip option for the T8i, so I'm not sure how "comfortable" it will be with some of the heftier lenses.

While personally I'd want the fastest zoom possible... f/2.8... to shoot sports indoors, you mention light in your gym is pretty good. So to save size and weight might want to consider a Canon EF 24-105mm f/4L lens and EF 70-200mm f/4L IS USM II. The 24-105mm would be a bit more versatile than a 24-7- thanks to the 30mm longer telephoto focal lengths in it's zoom range. Or, if you felt the need for a longer lens, the 70-200mm might serve well. Both these are a stop faster than your 18-55mm at it's 55mm setting, but a stop slower than the f/2.8 lenses above.

Compare with the above lenses:

EF 24-105mm f/4L IS USM II ($1099), approx. 3.25" x 4.75", 795 grams (28.5 oz.)
EF 70-200mm f/4L IS USM II ($1299), approx. 3.15" x 7", 780 grams (27.5 oz.)

Note: The EF 70-200mm f/4 lenses do not include a tripod mounting ring. It's sold separately, if wanted. But it's also part of the reason the f/4 lens appears so much lighter than the f/2.8 version. Canon Tripos Ring AII(WII) for the above f/4 lens costs $165 and adds about 140 grams (5 oz.) to the weight of the lens. Of course, when not needed it can be removed to lighten the lens and make it more compact.

I hope this helps with your decision!