For most sports use we would now recommend an autofocus binocular as they neatly side step the need for constant re-focusing as the action moves to and fro. You also don't want too much magnification or you'll be viewing individual horses instead of the pack (or viewing a player instead of the action going on around him)! It also really helps to try to keep them light so you don't get tired from raising and holding them to your eyes.
For most sports use a 7x 35 autofocus binocular is a good mix of optical characteristics and practical size so you can easily carry it around or fit in your pack. The wider angle models can also be useful to ensure you're not missing that fast horse now making a dash from behind or how a team member is shifting positionto set up an opportunity.
Note that with autofocus binoculars everything is focused from about 20 yards or so onwards (it depends on the make and model). You won't be able to use them for close up observation nor will you be able to use them if you have significant imbalance of vision between your eyes as they assume users have balanced eyesight. You don't need to be a full 20/20 but reasonably well balanced to get good use from them.
While the 7x 35 types tend to be our favourites there are other configurations for those who need a closer view or a less wide-angle view and of course the standard types of binoculars do allow for those who do have imbalannced eyesight.