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. Check out these examples:

• 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.

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:

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:

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.

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. Check out these examples:

• I’m throwing a kickoff party for his first game.

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. Check out these examples:

• 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.