It’s important to remember that you can use surprise witnesses to your advantage, often to establish industry standards or relatively innocuous facts unrelated to their direct examination. For example, I was once involved in a complex insurance-coverage case that intersected issues of a toxic substance exposure, multi-state contract interpretation, and choice-of-law issues that turned on whether the location of the exposure took place on a movable drilling rig. It was like a scary law school exam. Even though the other side called a surprise witness to talk about facts relating to the contract, he had a background in drilling and was able to provide helpful testimony on the ins and outs of the drilling industry. This helped us demonstrate the movability of the drilling rig to the court, which was a major issue that could preclude insurance coverage for the entire event. We used this witness to help establish facts that were helpful to our coverage case, even though he wasn’t too helpful on the contract issue. In short, determine whether the surprise witness can provide “vanilla” facts—those that seem or are truly innocuous as far as the witness is concerned, but those that may help your case in the end.
Finally, remember the points you need to score. You cannot always prevent surprise testimony from coming out and you may not be able to anticipate everything. But you can nail down facts that are well within this person’s knowledge or, conversely, rule them out. You can also get them to agree that they never surfaced before trial. This last point is risky—you certainly don’t want to highlight the fact that you did not depose this witness (or worse!). But if this witness failed to come forward earlier or has other baggage, that’s certainly proper fodder for cross-examination. Regardless, get in and get out, score your points, and try to minimize damage.
If and when you get to call your own surprise witness, the fun can really begin. You should know what this witness can and will say on the stand, both on direct and cross examination. Usually you can minimize your opponent’s efforts on redirect by asking whether anything said in cross changes their original testimony (spoiler alert: It should not).
Remember to keep your cool and stick to the facts you need to prove.