Thuogh sometime referred to as an adjective, kick-off in the usage you are showing is more properly an ***[attributive noun][1]***:

> Attributive here means "joined directly to a noun in order to describe it."
>
> So what distinguishes attributive nouns from adjectives? The categorization can be tricky, but here are two general rules:
>
> 1. An attributive noun can only modify a noun when it comes immediately before it: It's a business meeting, not a meeting that is business.
>
> 2. Attributive nouns don't have comparative forms, but many adjectives do: One building can be taller or more impressive than another, but it can't be more apartment than another.

(MerrianWebster.com)

From the [Grammarist][2]:

> Kick-off is also an adjective that describes a noun that comes first. It can be something in a sports event, meeting, seminar, etc. 
>
> - *The kick-off event was a 90-minute lecture by Bill Gates.*

From: [writingexplained.org][3]:

> As an adjective, kickoff describes something that comes first, whether the first play in a sporting event, the first seminar in a professional conference, or many other things.
>
> - *Jen and Mark threw a kick-off party to celebrate their son’s first game in the NFL.* 


  [1]: https://www.merriam-webster.com/words-at-play/nouns-that-look-like-adjectives#:~:text=An%20attributive%20noun%20is%20a,an%20apartment%20building
  [2]: https://grammarist.com/spelling/kick-off-kickoff/#:~:text=Kick%2Doff%20is%20also%20an,party%20for%20his%20first%20game.
  [3]: https://writingexplained.org/kickoff-or-kick-off