Matrix Field: How to disable specific rows?

Is there a way to block specific rows in specific columns? 

There is not a feature to disable rows or columns in the matrix field; however, injecting some CSS code could help you to achieve it. 

For example, if you need to disable the first row of fields you could inject this code: 

.form-matrix-table tr:nth-child(2) td input {

    pointer-events: none;

}

If you would need to apply the code to a different row then you would only need to change the number in the "nth-child" selector, it starts in 2 since the first row contains the column headers. 

This guide will help you to inject the given code to your form: https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes 

Hope this helps.

Thanks for the reply! Is there a way to block a single radio button? Like say, column 4, row 3?

You need to find the ids of the field https://www.jotform.com/help/146-How-to-find-field-IDs-and-names and then apply the css to individual field

If you face any issue then let us know the form and the specific field you are having trouble with.