Which of the following constitutes a federal civil suit under Section 1983?

A federal civil suit under Section 1983 pertains to the enforcement of civil rights when a person acting under the color of state law violates another person's rights. Excessive force causing pain is a clear instance where civil rights may have been violated, as it involves law enforcement or government officials using more force than is reasonably necessary to carry out their duties. In this scenario, the individual whose rights have been infringed can file a lawsuit under Section 1983, seeking redress for the violation of their constitutional rights.

The other options presented do not inherently constitute a federal civil suit under Section 1983. The use of unlicensed weapons may raise questions regarding legality and regulations but does not directly relate to a constitutional rights violation. Loose administrative practices could indicate poor governance or inefficiency but do not typically reflect a singular violation of civil rights. Tort liability cases are generally civil claims for damages that arise from wrongful acts, but they are not specific to constitutional rights and thus do not fit the framework of Section 1983 lawsuits. Hence, excessive force causing pain stands out as the appropriate situation that justifies a federal civil suit under this statute.