[Vocabulary] Size of the dog /fight in the dog - Meaning

[Kumar Nadimuthu]

Shastri went on to say that Kohli's turnaround since his disastrous tour of England, where he averaged 13.4 in five Tests, had been exceptional. "He showed that it's not the size of the dog in fight that matters, it's the fight in the dog that counts," he said.

What is the meaning of underlined part?

 

[Rover_KE]

What is the source of this quotation?

 

[Kumar Nadimuthu]

What is the source of this quotation?

Cricbuzz

Here is a link:http://www.cricbuzz.com/cricket-ser...i-defends-kohli-lauds-team-indias-performance

 

[SoothingDave]

Victory in a competition is not always determined by the competitor who is the biggest/strongest/fastest/smartest, etc. It is often determined by which competitor has the most dedication, determination, tenacity.

So it is not the size of the dog in the fight that is important, but rather the size of the "fight" in the dog.