We're very fortunate in Canada to actually have very effective vaccines. However, vaccines are not 100% effective even with two doses.
To illustrate this, if a vaccine is 80% effective, you might still get a fifth of the population, even after vaccination, who may be susceptible to infection. What we do know, in general, is that these infections are going to be milder, so the prevention of serious outcomes is also very key.
You've brought up a very important point, which is that you can still get infected. Even though you have a mild illness, you could pass it on to someone else who might not have been well vaccinated. The bottom line still stays the same, whether it's the variants we have now, or the fact you may still see cases after vaccination. The bottom line is to get two doses of a vaccine, or to complete a full course of vaccines. That will still work.
Sports teams have to have protocols. At this time, these types of games are performed under the auspices of public health departments that have safety plans in place so that, should people become positive, they don't spread that virus to a lot of other people.