Ambiguity of "to be" + gerund

I would like to ask about a basic sentence that really confuses me.

My favorite sport is swimming.

I think it is strange. "Swimming" can be interpreted as a gerund ("I like to swim; it is my favorite sport") but also as a verb ("What my favorite sport does is swim"). I would like to resolve the ambiguity, so swimming can only be interpreted as a gerund. How do I go about that?

There is nothing to correct. In that sentence swimming is a noun, just as football, for example, would be.

Rather than use the term gerund, I find it more helpful to describe a word such as swimming as the ‘-ing’ form of the verb and then go on to identify the role it plays in the clause under consideration. In your example it is, as I have said, a noun and is the subject predicative, or complement of is. It can also occur as a verb and an as adjective. As a verb, it is used to form the present progressive construction to indicate a current event, as in, for example I am swimming. As an adjective it can modify a noun, as in swimming birds. This use has to be distinguished from something like swimming club, in which swimming is a noun modifying another noun.

English has all sorts of ambiguities like this. (I suspect most other languages do too.) Usually the correct meaning is clear from context. If not, you have to rewrite the sentence, sometimes drastically.

"My favorite sport is swimming" is unlikely to cause confusion. It's hard to see how a sport can swim, so it's pretty obvious that the gerund is intended.

tchrist did come up with a couple of sentences where it might truly be ambiguous. "My favorite sport is boring my wife." The writer could mean that the sport that he most enjoys is not interesting to his wife, like he enjoys watching football but she thinks that football is boring. Or he could mean that the thing he mosts likes to do is to make his wife feel bored, that they often have conversations where he drones on for hours about subjects that do not interest her. The second meaning is likely a joke or a sarcastic comment, but it is a plausible interpretation of the sentence. (This is the kind of ambiguity that is the basis for many jokes.)

The intended meaning would often be made clear from the larger context. Like if you said, "I really love football. I spend hours a day watching it on TV and reading about it. But my wife hates it. My favorite sport is boring my wife." Then the first meaning is likely intended. But, "My marriage has sunk into a dull sameness. The only pleasure I get these days is the victory of knowing that I am making her even more depressed than I am. My favorite sport is boring my wife." In that the second meaning is meant.

You could reword the sentence to eliminate the ambiguity. Like, "My wife finds my favorite sport boring" versus "Boring my wife is my favorite sport."