I've been calling
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.
more information: present perfect continuous tense
Notice that an is used instead of 'a' before words that begin with a vowel sound. Follow the link to find out more.
more information: a & an
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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Seen is the past participle of the irregular verb see. Follow the link below to find out more and to listen to some examples.
more information: see
let your hair down
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.
Click here for more idioms and common expressions.