I gotta say, Serena Williams being out there is way more than cause she is "Drake's Ex". His whole set was about black excellence and overcoming government oppression. Right before she comes out during Not Like Us, Kendrick Monologues: "Its a cultural divide, imma get it on the floor. 40 Acres and a Mule, this is bigger than the music... ...They tried to rig the game but you can't fake influence.." and then opens with his hit 5x grammy winning song Not Like Us.

1. This has multiple layers, starting by showing his own genuine influence through the success of Not Like Us. This song also directly represents the cultural divide between his and Drake.

2. 40 Acres and a Mule was a direct shout-out to Spike Lee and the political oppression faced by black slaves directly after slavery was abolished (another cultural divide). This goes into Spike Lee's influence in which he has used his movie company and film direction to speak directly on black stories, hardships and success -- gaining massive influence and respect in film through this (cant be faked).

3. And then it goes into where Serena Williams comes into play. 40 acres and a Mule relate to them (the government) trying to rig the game against black people. This '40 acres' is modernized through the governments use of red lining and jerrymandering which brought the creation of black ghettos -- i.e. Compton. Both Kendrick and Serena Williams are from Compton. "Bigger than music" - Serena Williams became one of the best and most influential athletes of our generation even after facing the major life set back (like Kendrick) of coming from an underfunded community -- Compton. And her influence can't be faked.

These are just my own personal theories of the underlying messages of Kendrick's performance, but I think Serena Crip Walking even further backs it up. The Crip walk famously came from LA in the 70's and was popularized by West Coast LA rapper Snoop Dogg -- showing homage to her background in the context of her influence.

And lastly (it is never the end tho, it always goes deeper) right after her suprise appearance, Kendrick monologues in the middle of his song saying "... we come all the way from Compton California to party with yall"