Company: RSI
Filing Date: 2025-04-21
Form Type: DEFA14A
Source: 0001628280-25-018664
Chunk: 0

Company: Rush Street Interactive, Inc.
Filing Date: 2025-04-21
Form: DEFA14A
Chunk 0
---
<div align='center'>F</div>

### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

#### SCHEDULE 14A

#### Proxy Statement Pursuant to Section 14(a) of the
<div align='center'>Securities Exchange Act of 1934 (Amendment No. __)</div>

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

Check the appropriate box:

| ☐ |     | Preliminary Proxy Statement                                                     |
| ☐ |     | Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) |
| ☐ |     | Definitive Proxy Statement                                                      |
| ☒ |     | Definitive Additional Materials                                                 |
| ☐ |     | Soliciting Material under §240.14a-12                                           |

#### Rush Street Interactive, Inc.
<div align='center'>(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)</div>

Payment of Filing Fee (Check all boxes that apply):

| ☒ |     | No fee required                                                                                     |
| ☐ |     | Fee paid previously with preliminary materials                                                      |
| ☐ |     | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11 |