That's a horrible definition. Far too subjective. As a former (?) lawyer, you should be keenly aware the definition didn't work for them, and doesn't work for you (or me). If either of us can randomly determine when a hitter is "clutch" it takes all meaning from the word and leaves it as a bare bones concept at best.
And maybe coaches and players can recognize it, but our observational skills aren't as tuned in as theirs. And it's not like we talk to them about it.
Bottom line is, if you can't even tell me what a clutch hitter is, how can you know enough to recognize one?