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