Unlike many modern advocates of non-violence, Sprinkle has a largely orthodox set of beliefs. He recognizes the reality of hell (he co-authored the book Erasing Hell with Francis Chan, see my review here) and speaks without apology of God's wrath. I fear that it is too easy to dismiss many writers as leftist cranks without genuine interaction with their concerns. Unfortunately a lot of the literature on non-violence is muddied by authors who subscribe to heterodox positions like open theism. This makes their argument convenient to dismiss out of hand. After all if someone can get those kinds of issues wrong why would anyone give credence to much more complex questions.
Along with the typical New Testament passages, Sprinkle also looks at the Old Testament and the early church fathers. What he lays out is a convincing argument that non-violence is a normative and necessary outliving of the command to love our enemies. Also powerful is his wrestling with the usual "gotcha" questions like "what about Hitler?" and the hypothetical intruder bent on hurting your family. Those sorts of questions (I get them whenever I write on the topic on non-violence) are not designed to generate meaningful dialogue, they are designed to shut down conversation before it gets uncomfortable. Sprinkle approaches these topics with humility but conviction and his conclusions and thought process are worthwhile for every serious Bible student.
If there is a weakness in Fight it would be the narrowness of the topic. That is understandable but unfortunate. I prefer the broader term "non-resistance" to the more narrowly focused "non-violence". What we find in the New Testament is much broader than not shooting/beating up our enemies. Instead we see this idea of deferring to others in all sorts of aspects of our lives: economic, legal, etc. I get why Sprinkle focused as he did on violence proper (it is a huge problem in the Western church) but I would love to see him write a follow-up with a broader view.
Regardless of where you are currently on this subject Fight is a great entry to help the conversation. The non-violence position is a historical powerful witness and one that needs to be recovered in a church at ease with celebrating warfare and violence.