He means that he has called races in the past, is calling them now and will contiinue to call them in the future. For more about the present perfect continuous tense, follow the link.
Notice that an is used instead of 'a' before words that begin with a vowel sound. Follow the link to find out more.
It's absolutely to die for
If something is to die for it is extremely desirable.
Example: She makes cake that are to die for.
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To let your hair down is to relax and enjoy yourself after not being able to for a time.
Example: I like to let my hair down on the weekends.
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