Unusual and eccentric; offbeat

What a strange idea you've got! It's really out in left field but I like it

Che strana idea hai avuto! È veramente eccentrica, ma mi piace

 His theory about teaching a foreign language without ever mentioning grammar it's kind of far out, but sometimes it could work

La sua teoria sull'insegnamento di una lingua straniera senza mai nemmeno nominare la grammatica, è quantomeno singolare, ma a volte potrebbe anche funzionare

This idiom certainly comes from the world of baseball, but the exact allusion to left field is uncertain. According to one theory, in many early ball-parks left field was larger than right field, so it was easier to lose balls and generate confusion in left field