。
A good coach is like a parent to their players.
Literal
Good coach [topic-は] so-to-speak-いわば players [of-の] parent [like-のよう-なものだ].
いわば ('so to speak, as it were') is a formal rhetorical hedge introducing a metaphor or analogy. ~のようなものだ ('something like X') is the nominal-simile pattern, often used as a soft analogy. The whole sentence is a sentimental observation.