Ogresmasher gives a higher chance of knockback

doc/fixes3-7-0.txt

@@ -1513,6 +1513,7 @@ Grimtooth is permanently poisoned, protects from poison, and can fling poison
 cursed magic whistle can teleport you to your pet
 Fire and Frost Brand can be invoked for expert level fireball or cone of cold
 wielding Trollsbane grants hungerless regeneration
+hitting with Ogresmasher gives a higher chance of knockback
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

src/uhitm.c

@@ -5198,14 +5198,17 @@ mhitm_knockback(
     const char *knockedhow;
     coordxy dx, dy, defx, defy;
     int knockdistance = rn2(3) ? 1 : 2; /* 67%: 1 step, 33%: 2 steps */
+    int chance = 6; /* 1/6 chance of attack knocking back a monster */
     boolean u_agr = (magr == &gy.youmonst);
     boolean u_def = (mdef == &gy.youmonst);
     boolean was_u = FALSE, dismount = FALSE;
     struct obj *wep = weapon_used ? (u_agr ? uwep : MON_WEP(magr))
                                   : (struct obj *)0;
 
-    /* 1/6 chance of attack knocking back a monster */
-    if (rn2(6))
+    if (wep && is_art(wep, ART_OGRESMASHER))
+        chance = 2;
+
+    if (rn2(chance))
         return FALSE;
 
     /* decide where the first step will place the target; not accurate