The short answer is - it depends on what type of NDA you signed.
When the client posted their project, they were given the option to permit participants to display their proposed entries in their portfolios (whether or not they were selected as the winner in the project). If the client declined and did not allow participants to display their work in their portfolio, then the NDA in the project prevents you from legally doing so.
If you want to show that work in your portfolio (on crowdspring or elsewhere), you must first remove all identifying information about the client and/or the project.
Many clients allow creatives to display winning and non-winning work in their portfolios. In such projects, the NDA expressly lets you display your work in your portfolio.