- I got $30 gold bet against you, so don't let me down.
- Four!

6 seconds sound clip from the Back to the Future Part III movie soundboard.

You can hear this line at 01:22:35.608 in the DVD version of the movie.

Quote context

[...]

- Listen. I'm not really feeling up to this today. So I'm gonna have to forfeit.

- Forfeit? What's that mean?

- It means that you win without a fight.

- Without shooting? He can't do that. Hey, you can't do that!

- You know what I think? I think you ain't nothing but a gutless, yellow turd! And I'm giving you to the count of 10 to come out here and prove I'm wrong! One!

- Doc, come on, sober up, buddy. Let's go. Come on.

- You better get out there, son. I got $20 gold bet on you, so don't let me down.

- Three!

- I got $30 gold bet against you, so don't let me down.

- Four!

- You better face up to it, son, because if you don't go out there...

- What?

- Five!

- What if I don't go out there?

- You're a coward.

- And you'll be branded a coward for the rest of your days!

- Everybody everywhere will say Clint Eastwood is the biggest yellow belly in the West!

- Seven!

[...]