Sentence Correction

Hi instructors,

my question is about gerunds, I don't quite understand the differences between the sentences below:

Suspect: I like Mike swimming

Right: Mike swimming is a sight to be hold.

The explanation is "a noun preceding a gerund must be in the possessive case if the noun is the doer of the action described by the gerund".

Why " Mike swimming" in the first sentence is suspect, while in the second one is right?

Thanks.