But generally, "detta" fits better with indefinite nouns and "det här" better with definite ones, right?
Yes, den här takes the definite: ’det här laget’, but detta takes the indefinite: ’detta lag’ and the latter is more formal. However, in southern and western Sweden, you can also say detta laget which is equal to det här laget in speech, but you can write det här laget but not detta laget. As a summary:
- Det här laget: spoken and written form.
- Detta lag: primarily written form, not used much in speech.
- Detta laget: only spoken form (dialectal).
I think this sentence could also mean "This is a good law," right? But I suppose it makes sense for it not to have been counted since this is a section about sports.
It can't actually, since that kind of lag is an en word. So that would be Detta är en bra lag. One of the rare occasions when having two genders is useful :)