There are two different constructions merged in this example. Shifting the subject of the sentence to the right is perfectly normal both in speech and in writing, putting more emphasis on the description than the usual, and dull, Tendulkar is a great ambassador for the game.
The redundant is, on the other hand, is strictly incorrect
but not uncommon in spoken English. It may be to improve the rhythm: it may be that the speaker is momentarily confused between the two (equally acceptable) choices He's a great ambassador, Tendulkar or A great ambassador for the game, is Tendulkar; it may be simple inattention, as in The thing is, is that...
Bear in mind also that cricket commentators have to hold the audience's attention for several hours discussing a single game, so are usually accorded some latitude both in use of language and in relevance of topic (Test Match Special had a famously long-running discussion on cake, between balls, overs, or even sessions).