If sport on Sunday were no harm, Christ would have said so.

The Catholic Answers

Let us put it the other way round. If it were sinful, it is possible that Christ would have said so. We certainly cannot expect Him to describe all that is not sinful. Sleeping is not sinful, yet nowhere does Christ solemnly assure us that it is no sin to go to sleep. Christ omitted any explicit reference to sport on Sunday just as he omitted to refer to the wearing of shoes, sleeping at night, or the breathing of the air God gives us.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty