Effect
Hold Your Ground
Hold Your Ground is a defensive passive that offers a clear trade: you lose the ability to dodge, but in return your block chance rises sharply. For the Crusader, who is built around a shield and blocking anyway, that's an attractive bargain.
Since dodging is rarely a load-bearing defensive pillar for the Crusader, you give up little of value here. The added block chance, on the other hand, is high quality: it not only reduces incoming damage but also feeds the many block-based effects the Crusader uses across skills and items, such as Wrath generation or healing on block. In shield builds that make blocking a cornerstone, Hold Your Ground is therefore almost always worth a slot. Players running shieldless or with a pure damage focus barely benefit and should spend the slot elsewhere.
What the trade actually means
The passive takes away every chance to Dodge and gives you 30% Block Chance in return. The consequence goes further than the tooltip suggests: every effect that grants you Dodge Chance becomes useless with Hold Your Ground. So check your gear and other skills before picking the passive.
Hold Your Ground unlocks at level 40. While leveling it becomes worthwhile as soon as you play with a shield full-time.
Shield and Provoke as a package
Blessed Shield requires a shield and factors your shield's Block Chance into its Holy damage; the thrown shield also bounces to further enemies. Provoke taunts every enemy nearby so they briefly focus on you, generating Wrath in the process, and the more attacks target you, the more often the raised Block Chance comes into play.
Other companions
Iron Skin adds a window in which part of all incoming damage is absorbed on top of blocking. Akarat's Champion and Condemn supply the damage while Hold Your Ground carries the defense. Finery grants Strength per socketed gem and often sits as the second passive because it works without any condition.